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Advanced topics on using Google C++ Testing Framework
Updated May 5, 2014 by w...@google.com

Now that you have read Primer and learned how to write tests using Google Test, it's time to learn some new tricks. This document will show you more assertions as well as how to construct complex failure messages, propagate fatal failures, reuse and speed up your test fixtures, and use various flags with your tests.

More Assertions

This section covers some less frequently used, but still significant, assertions.

Explicit Success and Failure

These three assertions do not actually test a value or expression. Instead, they generate a success or failure directly. Like the macros that actually perform a test, you may stream a custom failure message into the them.

SUCCEED();

Generates a success. This does NOT make the overall test succeed. A test is considered successful only if none of its assertions fail during its execution.

Note: SUCCEED() is purely documentary and currently doesn't generate any user-visible output. However, we may add SUCCEED() messages to Google Test's output in the future.

FAIL(); ADD_FAILURE(); ADD_FAILURE_AT("file_path", line_number);

FAIL() generates a fatal failure, while ADD_FAILURE() and ADD_FAILURE_AT() generate a nonfatal failure. These are useful when control flow, rather than a Boolean expression, deteremines the test's success or failure. For example, you might want to write something like:

switch(expression) {
  case 1: ... some checks ...
  case 2: ... some other checks
  ...
  default: FAIL() << "We shouldn't get here.";
}

Note: you can only use FAIL() in functions that return void. See the Assertion Placement section for more information.

Availability: Linux, Windows, Mac.

Exception Assertions

These are for verifying that a piece of code throws (or does not throw) an exception of the given type:

Fatal assertion Nonfatal assertion Verifies
ASSERT_THROW(statement, exception_type); EXPECT_THROW(statement, exception_type); statement throws an exception of the given type
ASSERT_ANY_THROW(statement); EXPECT_ANY_THROW(statement); statement throws an exception of any type
ASSERT_NO_THROW(statement); EXPECT_NO_THROW(statement); statement doesn't throw any exception

Examples:

ASSERT_THROW(Foo(5), bar_exception);

EXPECT_NO_THROW({
  int n = 5;
  Bar(&n);
});

Availability: Linux, Windows, Mac; since version 1.1.0.

Predicate Assertions for Better Error Messages

Even though Google Test has a rich set of assertions, they can never be complete, as it's impossible (nor a good idea) to anticipate all the scenarios a user might run into. Therefore, sometimes a user has to use EXPECT_TRUE() to check a complex expression, for lack of a better macro. This has the problem of not showing you the values of the parts of the expression, making it hard to understand what went wrong. As a workaround, some users choose to construct the failure message by themselves, streaming it into EXPECT_TRUE(). However, this is awkward especially when the expression has side-effects or is expensive to evaluate.

Google Test gives you three different options to solve this problem:

Using an Existing Boolean Function

If you already have a function or a functor that returns bool (or a type that can be implicitly converted to bool), you can use it in a predicate assertion to get the function arguments printed for free:

Fatal assertion Nonfatal assertion Verifies
ASSERT_PRED1(pred1, val1); EXPECT_PRED1(pred1, val1); pred1(val1) returns true
ASSERT_PRED2(pred2, val1, val2); EXPECT_PRED2(pred2, val1, val2); pred2(val1, val2) returns true
... ... ...

In the above, predn is an n-ary predicate function or functor, where val1, val2, ..., and valn are its arguments. The assertion succeeds if the predicate returns true when applied to the given arguments, and fails otherwise. When the assertion fails, it prints the value of each argument. In either case, the arguments are evaluated exactly once.

Here's an example. Given

// Returns true iff m and n have no common divisors except 1.
bool MutuallyPrime(int m, int n) { ... }
const int a = 3;
const int b = 4;
const int c = 10;

the assertion EXPECT_PRED2(MutuallyPrime, a, b); will succeed, while the assertion EXPECT_PRED2(MutuallyPrime, b, c); will fail with the message

 !MutuallyPrime(b, c) is false, where
 b is 4
 c is 10
 

Notes:

  1. If you see a compiler error "no matching function to call" when using ASSERT_PRED* or EXPECT_PRED*, please see this for how to resolve it.
  2. Currently we only provide predicate assertions of arity <= 5. If you need a higher-arity assertion, let us know.

Availability: Linux, Windows, Mac

Using a Function That Returns an AssertionResult

While EXPECT_PRED*() and friends are handy for a quick job, the syntax is not satisfactory: you have to use different macros for different arities, and it feels more like Lisp than C++. The ::testing::AssertionResult class solves this problem.

An AssertionResult object represents the result of an assertion (whether it's a success or a failure, and an associated message). You can create an AssertionResult using one of these factory functions:

namespace testing {

// Returns an AssertionResult object to indicate that an assertion has
// succeeded.
AssertionResult AssertionSuccess();

// Returns an AssertionResult object to indicate that an assertion has
// failed.
AssertionResult AssertionFailure();

}

You can then use the << operator to stream messages to the AssertionResult object.

To provide more readable messages in Boolean assertions (e.g. EXPECT_TRUE()), write a predicate function that returns AssertionResult instead of bool. For example, if you define IsEven() as:

::testing::AssertionResult IsEven(int n) {
  if ((n % 2) == 0)
    return ::testing::AssertionSuccess();
  else
    return ::testing::AssertionFailure() << n << " is odd";
}

instead of:

bool IsEven(int n) {
  return (n % 2) == 0;
}

the failed assertion EXPECT_TRUE(IsEven(Fib(4))) will print:

   Value of: IsEven(Fib(4))
     Actual: false (*3 is odd*)
   Expected: true
 

instead of a more opaque

   Value of: IsEven(Fib(4))
     Actual: false
   Expected: true
 
If you want informative messages in EXPECT_FALSE and ASSERT_FALSE as well, and are fine with making the predicate slower in the success case, you can supply a success message:

::testing::AssertionResult IsEven(int n) {
  if ((n % 2) == 0)
    return ::testing::AssertionSuccess() << n << " is even";
  else
    return ::testing::AssertionFailure() << n << " is odd";
}

Then the statement EXPECT_FALSE(IsEven(Fib(6))) will print

   Value of: IsEven(Fib(6))
     Actual: true (8 is even)
   Expected: false
 

Availability: Linux, Windows, Mac; since version 1.4.1.

Using a Predicate-Formatter

If you find the default message generated by (ASSERT|EXPECT)_PRED* and (ASSERT|EXPECT)_(TRUE|FALSE) unsatisfactory, or some arguments to your predicate do not support streaming to ostream, you can instead use the following predicate-formatter assertions to fully customize how the message is formatted:

Fatal assertion Nonfatal assertion Verifies
ASSERT_PRED_FORMAT1(pred_format1, val1); EXPECT_PRED_FORMAT1(pred_format1, val1`); pred_format1(val1) is successful
ASSERT_PRED_FORMAT2(pred_format2, val1, val2); EXPECT_PRED_FORMAT2(pred_format2, val1, val2); pred_format2(val1, val2) is successful
... ... ...

The difference between this and the previous two groups of macros is that instead of a predicate, (ASSERT|EXPECT)_PRED_FORMAT* take a predicate-formatter (pred_formatn), which is a function or functor with the signature:

::testing::AssertionResult PredicateFormattern(const char* expr1, const char* expr2, ... const char* exprn, T1 val1, T2 val2, ... Tn valn);

where val1, val2, ..., and valn are the values of the predicate arguments, and expr1, expr2, ..., and exprn are the corresponding expressions as they appear in the source code. The types T1, T2, ..., and Tn can be either value types or reference types. For example, if an argument has type Foo, you can declare it as either Foo or const Foo&, whichever is appropriate.

A predicate-formatter returns a ::testing::AssertionResult object to indicate whether the assertion has succeeded or not. The only way to create such an object is to call one of these factory functions:

As an example, let's improve the failure message in the previous example, which uses EXPECT_PRED2():

// Returns the smallest prime common divisor of m and n,
// or 1 when m and n are mutually prime.
int SmallestPrimeCommonDivisor(int m, int n) { ... }

// A predicate-formatter for asserting that two integers are mutually prime.
::testing::AssertionResult AssertMutuallyPrime(const char* m_expr,
                                               const char* n_expr,
                                               int m,
                                               int n) {
  if (MutuallyPrime(m, n))
    return ::testing::AssertionSuccess();
 
  return ::testing::AssertionFailure()
      << m_expr << " and " << n_expr << " (" << m << " and " << n
      << ") are not mutually prime, " << "as they have a common divisor "
      << SmallestPrimeCommonDivisor(m, n);
}

With this predicate-formatter, we can use

EXPECT_PRED_FORMAT2(AssertMutuallyPrime, b, c);

to generate the message

 b and c (4 and 10) are not mutually prime, as they have a common divisor 2.
 

As you may have realized, many of the assertions we introduced earlier are special cases of (EXPECT|ASSERT)_PRED_FORMAT*. In fact, most of them are indeed defined using (EXPECT|ASSERT)_PRED_FORMAT*.

Availability: Linux, Windows, Mac.

Floating-Point Comparison

Comparing floating-point numbers is tricky. Due to round-off errors, it is very unlikely that two floating-points will match exactly. Therefore, ASSERT_EQ 's naive comparison usually doesn't work. And since floating-points can have a wide value range, no single fixed error bound works. It's better to compare by a fixed relative error bound, except for values close to 0 due to the loss of precision there.

In general, for floating-point comparison to make sense, the user needs to carefully choose the error bound. If they don't want or care to, comparing in terms of Units in the Last Place (ULPs) is a good default, and Google Test provides assertions to do this. Full details about ULPs are quite long; if you want to learn more, see this article on float comparison.

Floating-Point Macros

Fatal assertion Nonfatal assertion Verifies
ASSERT_FLOAT_EQ(expected, actual); EXPECT_FLOAT_EQ(expected, actual); the two float values are almost equal
ASSERT_DOUBLE_EQ(expected, actual); EXPECT_DOUBLE_EQ(expected, actual); the two double values are almost equal

By "almost equal", we mean the two values are within 4 ULP's from each other.

The following assertions allow you to choose the acceptable error bound:

Fatal assertion Nonfatal assertion Verifies
ASSERT_NEAR(val1, val2, abs_error); EXPECT_NEAR(val1, val2, abs_error); the difference between val1 and val2 doesn't exceed the given absolute error

Availability: Linux, Windows, Mac.

Floating-Point Predicate-Format Functions

Some floating-point operations are useful, but not that often used. In order to avoid an explosion of new macros, we provide them as predicate-format functions that can be used in predicate assertion macros (e.g. EXPECT_PRED_FORMAT2, etc).

EXPECT_PRED_FORMAT2(::testing::FloatLE, val1, val2);
EXPECT_PRED_FORMAT2(::testing::DoubleLE, val1, val2);

Verifies that val1 is less than, or almost equal to, val2. You can replace EXPECT_PRED_FORMAT2 in the above table with ASSERT_PRED_FORMAT2.

Availability: Linux, Windows, Mac.

Windows HRESULT assertions

These assertions test for HRESULT success or failure.

Fatal assertion Nonfatal assertion Verifies
ASSERT_HRESULT_SUCCEEDED(expression); EXPECT_HRESULT_SUCCEEDED(expression); expression is a success HRESULT
ASSERT_HRESULT_FAILED(expression); EXPECT_HRESULT_FAILED(expression); expression is a failure HRESULT

The generated output contains the human-readable error message associated with the HRESULT code returned by expression.

You might use them like this:

CComPtr shell;
ASSERT_HRESULT_SUCCEEDED(shell.CoCreateInstance(L"Shell.Application"));
CComVariant empty;
ASSERT_HRESULT_SUCCEEDED(shell->ShellExecute(CComBSTR(url), empty, empty, empty, empty));

Availability: Windows.

Type Assertions

You can call the function

::testing::StaticAssertTypeEq<T1, T2>();

to assert that types T1 and T2 are the same. The function does nothing if the assertion is satisfied. If the types are different, the function call will fail to compile, and the compiler error message will likely (depending on the compiler) show you the actual values of T1 and T2. This is mainly useful inside template code.

Caveat: When used inside a member function of a class template or a function template, StaticAssertTypeEq<T1, T2>() is effective only if the function is instantiated. For example, given:

template <typename T> class Foo {
 public:
  void Bar() { ::testing::StaticAssertTypeEq<int, T>(); }
};

the code:

void Test1() { Foo<bool> foo; }

will not generate a compiler error, as Foo<bool>::Bar() is never actually instantiated. Instead, you need:

void Test2() { Foo<bool> foo; foo.Bar(); }

to cause a compiler error.

Availability: Linux, Windows, Mac; since version 1.3.0.

Assertion Placement

You can use assertions in any C++ function. In particular, it doesn't have to be a method of the test fixture class. The one constraint is that assertions that generate a fatal failure (FAIL* and ASSERT_*) can only be used in void-returning functions. This is a consequence of Google Test not using exceptions. By placing it in a non-void function you'll get a confusing compile error like "error: void value not ignored as it ought to be".

If you need to use assertions in a function that returns non-void, one option is to make the function return the value in an out parameter instead. For example, you can rewrite T2 Foo(T1 x) to void Foo(T1 x, T2* result). You need to make sure that *result contains some sensible value even when the function returns prematurely. As the function now returns void, you can use any assertion inside of it.

If changing the function's type is not an option, you should just use assertions that generate non-fatal failures, such as ADD_FAILURE* and EXPECT_*.

Note: Constructors and destructors are not considered void-returning functions, according to the C++ language specification, and so you may not use fatal assertions in them. You'll get a compilation error if you try. A simple workaround is to transfer the entire body of the constructor or destructor to a private void-returning method. However, you should be aware that a fatal assertion failure in a constructor does not terminate the current test, as your intuition might suggest; it merely returns from the constructor early, possibly leaving your object in a partially-constructed state. Likewise, a fatal assertion failure in a destructor may leave your object in a partially-destructed state. Use assertions carefully in these situations!

Teaching Google Test How to Print Your Values

When a test assertion such as EXPECT_EQ fails, Google Test prints the argument values to help you debug. It does this using a user-extensible value printer.

This printer knows how to print built-in C++ types, native arrays, STL containers, and any type that supports the << operator. For other types, it prints the raw bytes in the value and hopes that you the user can figure it out.

As mentioned earlier, the printer is extensible. That means you can teach it to do a better job at printing your particular type than to dump the bytes. To do that, define << for your type:

#include <iostream>

namespace foo {

class Bar { ... };  // We want Google Test to be able to print instances of this.

// It's important that the << operator is defined in the SAME
// namespace that defines Bar.  C++'s look-up rules rely on that.
::std::ostream& operator<<(::std::ostream& os, const Bar& bar) {
  return os << bar.DebugString();  // whatever needed to print bar to os
}

}  // namespace foo

Sometimes, this might not be an option: your team may consider it bad style to have a << operator for Bar, or Bar may already have a << operator that doesn't do what you want (and you cannot change it). If so, you can instead define a PrintTo() function like this:

#include <iostream>

namespace foo {

class Bar { ... };

// It's important that PrintTo() is defined in the SAME
// namespace that defines Bar.  C++'s look-up rules rely on that.
void PrintTo(const Bar& bar, ::std::ostream* os) {
  *os << bar.DebugString();  // whatever needed to print bar to os
}

}  // namespace foo

If you have defined both << and PrintTo(), the latter will be used when Google Test is concerned. This allows you to customize how the value appears in Google Test's output without affecting code that relies on the behavior of its << operator.

If you want to print a value x using Google Test's value printer yourself, just call ::testing::PrintToString(x), which returns an std::string:

vector<pair<Bar, int> > bar_ints = GetBarIntVector();

EXPECT_TRUE(IsCorrectBarIntVector(bar_ints))
    << "bar_ints = " << ::testing::PrintToString(bar_ints);

Death Tests

In many applications, there are assertions that can cause application failure if a condition is not met. These sanity checks, which ensure that the program is in a known good state, are there to fail at the earliest possible time after some program state is corrupted. If the assertion checks the wrong condition, then the program may proceed in an erroneous state, which could lead to memory corruption, security holes, or worse. Hence it is vitally important to test that such assertion statements work as expected.

Since these precondition checks cause the processes to die, we call such tests death tests. More generally, any test that checks that a program terminates (except by throwing an exception) in an expected fashion is also a death test.

Note that if a piece of code throws an exception, we don't consider it "death" for the purpose of death tests, as the caller of the code could catch the exception and avoid the crash. If you want to verify exceptions thrown by your code, see Exception Assertions.

If you want to test EXPECT_*()/ASSERT_*() failures in your test code, see Catching Failures.

How to Write a Death Test

Google Test has the following macros to support death tests:

Fatal assertion Nonfatal assertion Verifies
ASSERT_DEATH(statement, regex`); EXPECT_DEATH(statement, regex`); statement crashes with the given error
ASSERT_DEATH_IF_SUPPORTED(statement, regex`); EXPECT_DEATH_IF_SUPPORTED(statement, regex`); if death tests are supported, verifies that statement crashes with the given error; otherwise verifies nothing
ASSERT_EXIT(statement, predicate, regex`); EXPECT_EXIT(statement, predicate, regex`); statement exits with the given error and its exit code matches predicate

where statement is a statement that is expected to cause the process to die, predicate is a function or function object that evaluates an integer exit status, and regex is a regular expression that the stderr output of statement is expected to match. Note that statement can be any valid statement (including compound statement) and doesn't have to be an expression.

As usual, the ASSERT variants abort the current test function, while the EXPECT variants do not.

Note: We use the word "crash" here to mean that the process terminates with a non-zero exit status code. There are two possibilities: either the process has called exit() or _exit() with a non-zero value, or it may be killed by a signal.

This means that if statement terminates the process with a 0 exit code, it is not considered a crash by EXPECT_DEATH. Use EXPECT_EXIT instead if this is the case, or if you want to restrict the exit code more precisely.

A predicate here must accept an int and return a bool. The death test succeeds only if the predicate returns true. Google Test defines a few predicates that handle the most common cases:

::testing::ExitedWithCode(exit_code)

This expression is true if the program exited normally with the given exit code.

::testing::KilledBySignal(signal_number)  // Not available on Windows.

This expression is true if the program was killed by the given signal.

The *_DEATH macros are convenient wrappers for *_EXIT that use a predicate that verifies the process' exit code is non-zero.

Note that a death test only cares about three things:

  1. does statement abort or exit the process?
  2. (in the case of ASSERT_EXIT and EXPECT_EXIT) does the exit status satisfy predicate? Or (in the case of ASSERT_DEATH and EXPECT_DEATH) is the exit status non-zero? And
  3. does the stderr output match regex?

In particular, if statement generates an ASSERT_* or EXPECT_* failure, it will not cause the death test to fail, as Google Test assertions don't abort the process.

To write a death test, simply use one of the above macros inside your test function. For example,

TEST(MyDeathTest, Foo) {
  // This death test uses a compound statement.
  ASSERT_DEATH({ int n = 5; Foo(&n); }, "Error on line .* of Foo()");
}
TEST(MyDeathTest, NormalExit) {
  EXPECT_EXIT(NormalExit(), ::testing::ExitedWithCode(0), "Success");
}
TEST(MyDeathTest, KillMyself) {
  EXPECT_EXIT(KillMyself(), ::testing::KilledBySignal(SIGKILL), "Sending myself unblockable signal");
}

verifies that:

  • calling Foo(5) causes the process to die with the given error message,
  • calling NormalExit() causes the process to print "Success" to stderr and exit with exit code 0, and
  • calling KillMyself() kills the process with signal SIGKILL.

The test function body may contain other assertions and statements as well, if necessary.

Important: We strongly recommend you to follow the convention of naming your test case (not test) *DeathTest when it contains a death test, as demonstrated in the above example. The Death Tests And Threads section below explains why.

If a test fixture class is shared by normal tests and death tests, you can use typedef to introduce an alias for the fixture class and avoid duplicating its code:

class FooTest : public ::testing::Test { ... };

typedef FooTest FooDeathTest;

TEST_F(FooTest, DoesThis) {
  // normal test
}

TEST_F(FooDeathTest, DoesThat) {
  // death test
}

Availability: Linux, Windows (requires MSVC 8.0 or above), Cygwin, and Mac (the latter three are supported since v1.3.0). (ASSERT|EXPECT)_DEATH_IF_SUPPORTED are new in v1.4.0.

Regular Expression Syntax

On POSIX systems (e.g. Linux, Cygwin, and Mac), Google Test uses the POSIX extended regular expression syntax in death tests. To learn about this syntax, you may want to read this Wikipedia entry.

On Windows, Google Test uses its own simple regular expression implementation. It lacks many features you can find in POSIX extended regular expressions. For example, we don't support union ("x|y"), grouping ("(xy)"), brackets ("[xy]"), and repetition count ("x{5,7}"), among others. Below is what we do support (Letter A denotes a literal character, period (.), or a single \\ escape sequence; x and y denote regular expressions.):

c matches any literal character c
\\d matches any decimal digit
\\D matches any character that's not a decimal digit
\\f matches \f
\\n matches \n
\\r matches \r
\\s matches any ASCII whitespace, including \n
\\S matches any character that's not a whitespace
\\t matches \t
\\v matches \v
\\w matches any letter, _, or decimal digit
\\W matches any character that \\w doesn't match
\\c matches any literal character c, which must be a punctuation
\\. matches the . character
. matches any single character except \n
A? matches 0 or 1 occurrences of A
A* matches 0 or many occurrences of A
A+ matches 1 or many occurrences of A
^ matches the beginning of a string (not that of each line)
$ matches the end of a string (not that of each line)
xy matches x followed by y

To help you determine which capability is available on your system, Google Test defines macro GTEST_USES_POSIX_RE=1 when it uses POSIX extended regular expressions, or GTEST_USES_SIMPLE_RE=1 when it uses the simple version. If you want your death tests to work in both cases, you can either #if on these macros or use the more limited syntax only.

How It Works

Under the hood, ASSERT_EXIT() spawns a new process and executes the death test statement in that process. The details of of how precisely that happens depend on the platform and the variable ::testing::GTEST_FLAG(death_test_style) (which is initialized from the command-line flag --gtest_death_test_style).

  • On POSIX systems, fork() (or clone() on Linux) is used to spawn the child, after which:
    • If the variable's value is "fast", the death test statement is immediately executed.
    • If the variable's value is "threadsafe", the child process re-executes the unit test binary just as it was originally invoked, but with some extra flags to cause just the single death test under consideration to be run.
  • On Windows, the child is spawned using the CreateProcess() API, and re-executes the binary to cause just the single death test under consideration to be run - much like the threadsafe mode on POSIX.

Other values for the variable are illegal and will cause the death test to fail. Currently, the flag's default value is "fast". However, we reserve the right to change it in the future. Therefore, your tests should not depend on this.

In either case, the parent process waits for the child process to complete, and checks that

  1. the child's exit status satisfies the predicate, and
  2. the child's stderr matches the regular expression.

If the death test statement runs to completion without dying, the child process will nonetheless terminate, and the assertion fails.

Death Tests And Threads

The reason for the two death test styles has to do with thread safety. Due to well-known problems with forking in the presence of threads, death tests should be run in a single-threaded context. Sometimes, however, it isn't feasible to arrange that kind of environment. For example, statically-initialized modules may start threads before main is ever reached. Once threads have been created, it may be difficult or impossible to clean them up.

Google Test has three features intended to raise awareness of threading issues.

  1. A warning is emitted if multiple threads are running when a death test is encountered.
  2. Test cases with a name ending in "DeathTest" are run before all other tests.
  3. It uses clone() instead of fork() to spawn the child process on Linux (clone() is not available on Cygwin and Mac), as fork() is more likely to cause the child to hang when the parent process has multiple threads.

It's perfectly fine to create threads inside a death test statement; they are executed in a separate process and cannot affect the parent.

Death Test Styles

The "threadsafe" death test style was introduced in order to help mitigate the risks of testing in a possibly multithreaded environment. It trades increased test execution time (potentially dramatically so) for improved thread safety. We suggest using the faster, default "fast" style unless your test has specific problems with it.

You can choose a particular style of death tests by setting the flag programmatically:

::testing::FLAGS_gtest_death_test_style = "threadsafe";

You can do this in main() to set the style for all death tests in the binary, or in individual tests. Recall that flags are saved before running each test and restored afterwards, so you need not do that yourself. For example:

TEST(MyDeathTest, TestOne) {
  ::testing::FLAGS_gtest_death_test_style = "threadsafe";
  // This test is run in the "threadsafe" style:
  ASSERT_DEATH(ThisShouldDie(), "");
}

TEST(MyDeathTest, TestTwo) {
  // This test is run in the "fast" style:
  ASSERT_DEATH(ThisShouldDie(), "");
}

int main(int argc, char** argv) {
  ::testing::InitGoogleTest(&argc, argv);
  ::testing::FLAGS_gtest_death_test_style = "fast";
  return RUN_ALL_TESTS();
}

Caveats

The statement argument of ASSERT_EXIT() can be any valid C++ statement. If it leaves the current function via a return statement or by throwing an exception, the death test is considered to have failed. Some Google Test macros may return from the current function (e.g. ASSERT_TRUE()), so be sure to avoid them in statement.

Since statement runs in the child process, any in-memory side effect (e.g. modifying a variable, releasing memory, etc) it causes will not be observable in the parent process. In particular, if you release memory in a death test, your program will fail the heap check as the parent process will never see the memory reclaimed. To solve this problem, you can

  1. try not to free memory in a death test;
  2. free the memory again in the parent process; or
  3. do not use the heap checker in your program.

Due to an implementation detail, you cannot place multiple death test assertions on the same line; otherwise, compilation will fail with an unobvious error message.

Despite the improved thread safety afforded by the "threadsafe" style of death test, thread problems such as deadlock are still possible in the presence of handlers registered with pthread_atfork(3).

Using Assertions in Sub-routines

Adding Traces to Assertions

If a test sub-routine is called from several places, when an assertion inside it fails, it can be hard to tell which invocation of the sub-routine the failure is from. You can alleviate this problem using extra logging or custom failure messages, but that usually clutters up your tests. A better solution is to use the SCOPED_TRACE macro:

SCOPED_TRACE(message);

where message can be anything streamable to std::ostream. This macro will cause the current file name, line number, and the given message to be added in every failure message. The effect will be undone when the control leaves the current lexical scope.

For example,

10: void Sub1(int n) {
11:   EXPECT_EQ(1, Bar(n));
12:   EXPECT_EQ(2, Bar(n + 1));
13: }
14: 
15: TEST(FooTest, Bar) {
16:   {
17:     SCOPED_TRACE("A");  // This trace point will be included in
18:                         // every failure in this scope.
19:     Sub1(1);
20:   }
21:   // Now it won't.
22:   Sub1(9);
23: }

could result in messages like these:

path/to/foo_test.cc:11: Failure
Value of: Bar(n)
Expected: 1
  Actual: 2
   Trace:
path/to/foo_test.cc:17: A

path/to/foo_test.cc:12: Failure
Value of: Bar(n + 1)
Expected: 2
  Actual: 3

Without the trace, it would've been difficult to know which invocation of Sub1() the two failures come from respectively. (You could add an extra message to each assertion in Sub1() to indicate the value of n, but that's tedious.)

Some tips on using SCOPED_TRACE:

  1. With a suitable message, it's often enough to use SCOPED_TRACE at the beginning of a sub-routine, instead of at each call site.
  2. When calling sub-routines inside a loop, make the loop iterator part of the message in SCOPED_TRACE such that you can know which iteration the failure is from.
  3. Sometimes the line number of the trace point is enough for identifying the particular invocation of a sub-routine. In this case, you don't have to choose a unique message for SCOPED_TRACE. You can simply use "".
  4. You can use SCOPED_TRACE in an inner scope when there is one in the outer scope. In this case, all active trace points will be included in the failure messages, in reverse order they are encountered.
  5. The trace dump is clickable in Emacs' compilation buffer - hit return on a line number and you'll be taken to that line in the source file!

Availability: Linux, Windows, Mac.

Propagating Fatal Failures

A common pitfall when using ASSERT_* and FAIL* is not understanding that when they fail they only abort the current function, not the entire test. For example, the following test will segfault:

void Subroutine() {
  // Generates a fatal failure and aborts the current function.
  ASSERT_EQ(1, 2);
  // The following won't be executed.
  ...
}

TEST(FooTest, Bar) {
  Subroutine();
  // The intended behavior is for the fatal failure
  // in Subroutine() to abort the entire test.
  // The actual behavior: the function goes on after Subroutine() returns.
  int* p = NULL;
  *p = 3; // Segfault!
}

Since we don't use exceptions, it is technically impossible to implement the intended behavior here. To alleviate this, Google Test provides two solutions. You could use either the (ASSERT|EXPECT)_NO_FATAL_FAILURE assertions or the HasFatalFailure() function. They are described in the following two subsections.

Asserting on Subroutines

As shown above, if your test calls a subroutine that has an ASSERT_* failure in it, the test will continue after the subroutine returns. This may not be what you want.

Often people want fatal failures to propagate like exceptions. For that Google Test offers the following macros:

Fatal assertion Nonfatal assertion Verifies
ASSERT_NO_FATAL_FAILURE(statement); EXPECT_NO_FATAL_FAILURE(statement); statement doesn't generate any new fatal failures in the current thread.

Only failures in the thread that executes the assertion are checked to determine the result of this type of assertions. If statement creates new threads, failures in these threads are ignored.

Examples:

ASSERT_NO_FATAL_FAILURE(Foo());

int i;
EXPECT_NO_FATAL_FAILURE({
  i = Bar();
});

Availability: Linux, Windows, Mac. Assertions from multiple threads are currently not supported.

Checking for Failures in the Current Test

HasFatalFailure() in the ::testing::Test class returns true if an assertion in the current test has suffered a fatal failure. This allows functions to catch fatal failures in a sub-routine and return early.

class Test {
 public:
  ...
  static bool HasFatalFailure();
};

The typical usage, which basically simulates the behavior of a thrown exception, is:

TEST(FooTest, Bar) {
  Subroutine();
  // Aborts if Subroutine() had a fatal failure.
  if (HasFatalFailure())
    return;
  // The following won't be executed.
  ...
}

If HasFatalFailure() is used outside of TEST() , TEST_F() , or a test fixture, you must add the ::testing::Test:: prefix, as in:

if (::testing::Test::HasFatalFailure())
  return;

Similarly, HasNonfatalFailure() returns true if the current test has at least one non-fatal failure, and HasFailure() returns true if the current test has at least one failure of either kind.

Availability: Linux, Windows, Mac. HasNonfatalFailure() and HasFailure() are available since version 1.4.0.

Logging Additional Information

In your test code, you can call RecordProperty("key", value) to log additional information, where value can be either a string or an int. The last value recorded for a key will be emitted to the XML output if you specify one. For example, the test

TEST_F(WidgetUsageTest, MinAndMaxWidgets) {
  RecordProperty("MaximumWidgets", ComputeMaxUsage());
  RecordProperty("MinimumWidgets", ComputeMinUsage());
}

will output XML like this:

...
  <testcase name="MinAndMaxWidgets" status="run" time="6" classname="WidgetUsageTest"
            MaximumWidgets="12"
            MinimumWidgets="9" />
...

Note:

  • RecordProperty() is a static member of the Test class. Therefore it needs to be prefixed with ::testing::Test:: if used outside of the TEST body and the test fixture class.
  • key must be a valid XML attribute name, and cannot conflict with the ones already used by Google Test (name, status, time, classname, type_param, and value_param).
  • Calling RecordProperty() outside of the lifespan of a test is allowed. If it's called outside of a test but between a test case's SetUpTestCase() and TearDownTestCase() methods, it will be attributed to the XML element for the test case. If it's called outside of all test cases (e.g. in a test environment), it will be attributed to the top-level XML element.

Availability: Linux, Windows, Mac.

Sharing Resources Between Tests in the Same Test Case

Google Test creates a new test fixture object for each test in order to make tests independent and easier to debug. However, sometimes tests use resources that are expensive to set up, making the one-copy-per-test model prohibitively expensive.

If the tests don't change the resource, there's no harm in them sharing a single resource copy. So, in addition to per-test set-up/tear-down, Google Test also supports per-test-case set-up/tear-down. To use it:

  1. In your test fixture class (say FooTest ), define as static some member variables to hold the shared resources.
  2. In the same test fixture class, define a static void SetUpTestCase() function (remember not to spell it as SetupTestCase with a small u!) to set up the shared resources and a static void TearDownTestCase() function to tear them down.

That's it! Google Test automatically calls SetUpTestCase() before running the first test in the FooTest test case (i.e. before creating the first FooTest object), and calls TearDownTestCase() after running the last test in it (i.e. after deleting the last FooTest object). In between, the tests can use the shared resources.

Remember that the test order is undefined, so your code can't depend on a test preceding or following another. Also, the tests must either not modify the state of any shared resource, or, if they do modify the state, they must restore the state to its original value before passing control to the next test.

Here's an example of per-test-case set-up and tear-down:

class FooTest : public ::testing::Test {
 protected:
  // Per-test-case set-up.
  // Called before the first test in this test case.
  // Can be omitted if not needed.
  static void SetUpTestCase() {
    shared_resource_ = new ...;
  }

  // Per-test-case tear-down.
  // Called after the last test in this test case.
  // Can be omitted if not needed.
  static void TearDownTestCase() {
    delete shared_resource_;
    shared_resource_ = NULL;
  }

  // You can define per-test set-up and tear-down logic as usual.
  virtual void SetUp() { ... }
  virtual void TearDown() { ... }

  // Some expensive resource shared by all tests.
  static T* shared_resource_;
};

T* FooTest::shared_resource_ = NULL;

TEST_F(FooTest, Test1) {
  ... you can refer to shared_resource here ...
}
TEST_F(FooTest, Test2) {
  ... you can refer to shared_resource here ...
}

Availability: Linux, Windows, Mac.

Global Set-Up and Tear-Down

Just as you can do set-up and tear-down at the test level and the test case level, you can also do it at the test program level. Here's how.

First, you subclass the ::testing::Environment class to define a test environment, which knows how to set-up and tear-down:

class Environment {
 public:
  virtual ~Environment() {}
  // Override this to define how to set up the environment.
  virtual void SetUp() {}
  // Override this to define how to tear down the environment.
  virtual void TearDown() {}
};

Then, you register an instance of your environment class with Google Test by calling the ::testing::AddGlobalTestEnvironment() function:

Environment* AddGlobalTestEnvironment(Environment* env);

Now, when RUN_ALL_TESTS() is called, it first calls the SetUp() method of the environment object, then runs the tests if there was no fatal failures, and finally calls TearDown() of the environment object.

It's OK to register multiple environment objects. In this case, their SetUp() will be called in the order they are registered, and their TearDown() will be called in the reverse order.

Note that Google Test takes ownership of the registered environment objects. Therefore do not delete them by yourself.

You should call AddGlobalTestEnvironment() before RUN_ALL_TESTS() is called, probably in main(). If you use gtest_main, you need to call this before main() starts for it to take effect. One way to do this is to define a global variable like this:

::testing::Environment* const foo_env = ::testing::AddGlobalTestEnvironment(new FooEnvironment);

However, we strongly recommend you to write your own main() and call AddGlobalTestEnvironment() there, as relying on initialization of global variables makes the code harder to read and may cause problems when you register multiple environments from different translation units and the environments have dependencies among them (remember that the compiler doesn't guarantee the order in which global variables from different translation units are initialized).

Availability: Linux, Windows, Mac.

Value Parameterized Tests

Value-parameterized tests allow you to test your code with different parameters without writing multiple copies of the same test.

Suppose you write a test for your code and then realize that your code is affected by a presence of a Boolean command line flag.

TEST(MyCodeTest, TestFoo) {
  // A code to test foo().
}

Usually people factor their test code into a function with a Boolean parameter in such situations. The function sets the flag, then executes the testing code.

void TestFooHelper(bool flag_value) {
  flag = flag_value;
  // A code to test foo().
}

TEST(MyCodeTest, TestFoo) {
  TestFooHelper(false);
  TestFooHelper(true);
}

But this setup has serious drawbacks. First, when a test assertion fails in your tests, it becomes unclear what value of the parameter caused it to fail. You can stream a clarifying message into your EXPECT/ASSERT statements, but it you'll have to do it with all of them. Second, you have to add one such helper function per test. What if you have ten tests? Twenty? A hundred?

Value-parameterized tests will let you write your test only once and then easily instantiate and run it with an arbitrary number of parameter values.

Here are some other situations when value-parameterized tests come handy:

  • You want to test different implementations of an OO interface.
  • You want to test your code over various inputs (a.k.a. data-driven testing). This feature is easy to abuse, so please exercise your good sense when doing it!

How to Write Value-Parameterized Tests

To write value-parameterized tests, first you should define a fixture class. It must be derived from both ::testing::Test and ::testing::WithParamInterface<T> (the latter is a pure interface), where T is the type of your parameter values. For convenience, you can just derive the fixture class from ::testing::TestWithParam<T>, which itself is derived from both ::testing::Test and ::testing::WithParamInterface<T>. T can be any copyable type. If it's a raw pointer, you are responsible for managing the lifespan of the pointed values.

class FooTest : public ::testing::TestWithParam<const char*> {
  // You can implement all the usual fixture class members here.
  // To access the test parameter, call GetParam() from class
  // TestWithParam<T>.
};

// Or, when you want to add parameters to a pre-existing fixture class:
class BaseTest : public ::testing::Test {
  ...
};
class BarTest : public BaseTest,
                public ::testing::WithParamInterface<const char*> {
  ...
};

Then, use the TEST_P macro to define as many test patterns using this fixture as you want. The _P suffix is for "parameterized" or "pattern", whichever you prefer to think.

TEST_P(FooTest, DoesBlah) {
  // Inside a test, access the test parameter with the GetParam() method
  // of the TestWithParam<T> class:
  EXPECT_TRUE(foo.Blah(GetParam()));
  ...
}

TEST_P(FooTest, HasBlahBlah) {
  ...
}

Finally, you can use INSTANTIATE_TEST_CASE_P to instantiate the test case with any set of parameters you want. Google Test defines a number of functions for generating test parameters. They return what we call (surprise!) parameter generators. Here is a summary of them, which are all in the testing namespace:

Range(begin, end[, step]) Yields values {begin, begin+step, begin+step+step, ...}. The values do not include end. step defaults to 1.
Values(v1, v2, ..., vN) Yields values {v1, v2, ..., vN}.
ValuesIn(container) and ValuesIn(begin, end) Yields values from a C-style array, an STL-style container, or an iterator range [begin, end). container, begin, and end can be expressions whose values are determined at run time.
Bool() Yields sequence {false, true}.
Combine(g1, g2, ..., gN) Yields all combinations (the Cartesian product for the math savvy) of the values generated by the N generators. This is only available if your system provides the <tr1/tuple> header. If you are sure your system does, and Google Test disagrees, you can override it by defining GTEST_HAS_TR1_TUPLE=1. See comments in include/gtest/internal/gtest-port.h for more information.

For more details, see the comments at the definitions of these functions in the source code.

The following statement will instantiate tests from the FooTest test case each with parameter values "meeny", "miny", and "moe".

INSTANTIATE_TEST_CASE_P(InstantiationName,
                        FooTest,
                        ::testing::Values("meeny", "miny", "moe"));

To distinguish different instances of the pattern (yes, you can instantiate it more than once), the first argument to INSTANTIATE_TEST_CASE_P is a prefix that will be added to the actual test case name. Remember to pick unique prefixes for different instantiations. The tests from the instantiation above will have these names:

  • InstantiationName/FooTest.DoesBlah/0 for "meeny"
  • InstantiationName/FooTest.DoesBlah/1 for "miny"
  • InstantiationName/FooTest.DoesBlah/2 for "moe"
  • InstantiationName/FooTest.HasBlahBlah/0 for "meeny"
  • InstantiationName/FooTest.HasBlahBlah/1 for "miny"
  • InstantiationName/FooTest.HasBlahBlah/2 for "moe"

You can use these names in --gtest_filter.

This statement will instantiate all tests from FooTest again, each with parameter values "cat" and "dog":

const char* pets[] = {"cat", "dog"};
INSTANTIATE_TEST_CASE_P(AnotherInstantiationName, FooTest,
                        ::testing::ValuesIn(pets));

The tests from the instantiation above will have these names:

  • AnotherInstantiationName/FooTest.DoesBlah/0 for "cat"
  • AnotherInstantiationName/FooTest.DoesBlah/1 for "dog"
  • AnotherInstantiationName/FooTest.HasBlahBlah/0 for "cat"
  • AnotherInstantiationName/FooTest.HasBlahBlah/1 for "dog"

Please note that INSTANTIATE_TEST_CASE_P will instantiate all tests in the given test case, whether their definitions come before or after the INSTANTIATE_TEST_CASE_P statement.

You can see these files for more examples.

Availability: Linux, Windows (requires MSVC 8.0 or above), Mac; since version 1.2.0.

Creating Value-Parameterized Abstract Tests

In the above, we define and instantiate FooTest in the same source file. Sometimes you may want to define value-parameterized tests in a library and let other people instantiate them later. This pattern is known as abstract tests. As an example of its application, when you are designing an interface you can write a standard suite of abstract tests (perhaps using a factory function as the test parameter) that all implementations of the interface are expected to pass. When someone implements the interface, he can instantiate your suite to get all the interface-conformance tests for free.

To define abstract tests, you should organize your code like this:

  1. Put the definition of the parameterized test fixture class (e.g. FooTest) in a header file, say foo_param_test.h. Think of this as declaring your abstract tests.
  2. Put the TEST_P definitions in foo_param_test.cc, which includes foo_param_test.h. Think of this as implementing your abstract tests.

Once they are defined, you can instantiate them by including foo_param_test.h, invoking INSTANTIATE_TEST_CASE_P(), and linking with foo_param_test.cc. You can instantiate the same abstract test case multiple times, possibly in different source files.

Typed Tests

Suppose you have multiple implementations of the same interface and want to make sure that all of them satisfy some common requirements. Or, you may have defined several types that are supposed to conform to the same "concept" and you want to verify it. In both cases, you want the same test logic repeated for different types.

While you can write one TEST or TEST_F for each type you want to test (and you may even factor the test logic into a function template that you invoke from the TEST), it's tedious and doesn't scale: if you want m tests over n types, you'll end up writing m*n TESTs.

Typed tests allow you to repeat the same test logic over a list of types. You only need to write the test logic once, although you must know the type list when writing typed tests. Here's how you do it:

First, define a fixture class template. It should be parameterized by a type. Remember to derive it from ::testing::Test:

template <typename T>
class FooTest : public ::testing::Test {
 public:
  ...
  typedef std::list<T> List;
  static T shared_;
  T value_;
};

Next, associate a list of types with the test case, which will be repeated for each type in the list:

typedef ::testing::Types<char, int, unsigned int> MyTypes;
TYPED_TEST_CASE(FooTest, MyTypes);

The typedef is necessary for the TYPED_TEST_CASE macro to parse correctly. Otherwise the compiler will think that each comma in the type list introduces a new macro argument.

Then, use TYPED_TEST() instead of TEST_F() to define a typed test for this test case. You can repeat this as many times as you want:

TYPED_TEST(FooTest, DoesBlah) {
  // Inside a test, refer to the special name TypeParam to get the type
  // parameter.  Since we are inside a derived class template, C++ requires
  // us to visit the members of FooTest via 'this'.
  TypeParam n = this->value_;

  // To visit static members of the fixture, add the 'TestFixture::'
  // prefix.
  n += TestFixture::shared_;

  // To refer to typedefs in the fixture, add the 'typename TestFixture::'
  // prefix.  The 'typename' is required to satisfy the compiler.
  typename TestFixture::List values;
  values.push_back(n);
  ...
}

TYPED_TEST(FooTest, HasPropertyA) { ... }

You can see samples/sample6_unittest.cc for a complete example.

Availability: Linux, Windows (requires MSVC 8.0 or above), Mac; since version 1.1.0.

Type-Parameterized Tests

Type-parameterized tests are like typed tests, except that they don't require you to know the list of types ahead of time. Instead, you can define the test logic first and instantiate it with different type lists later. You can even instantiate it more than once in the same program.

If you are designing an interface or concept, you can define a suite of type-parameterized tests to verify properties that any valid implementation of the interface/concept should have. Then, the author of each implementation can just instantiate the test suite with his type to verify that it conforms to the requirements, without having to write similar tests repeatedly. Here's an example:

First, define a fixture class template, as we did with typed tests:

template <typename T>
class FooTest : public ::testing::Test {
  ...
};

Next, declare that you will define a type-parameterized test case:

TYPED_TEST_CASE_P(FooTest);

The _P suffix is for "parameterized" or "pattern", whichever you prefer to think.

Then, use TYPED_TEST_P() to define a type-parameterized test. You can repeat this as many times as you want:

TYPED_TEST_P(FooTest, DoesBlah) {
  // Inside a test, refer to TypeParam to get the type parameter.
  TypeParam n = 0;
  ...
}

TYPED_TEST_P(FooTest, HasPropertyA) { ... }

Now the tricky part: you need to register all test patterns using the REGISTER_TYPED_TEST_CASE_P macro before you can instantiate them. The first argument of the macro is the test case name; the rest are the names of the tests in this test case:

REGISTER_TYPED_TEST_CASE_P(FooTest,
                           DoesBlah, HasPropertyA);

Finally, you are free to instantiate the pattern with the types you want. If you put the above code in a header file, you can #include it in multiple C++ source files and instantiate it multiple times.

typedef ::testing::Types<char, int, unsigned int> MyTypes;
INSTANTIATE_TYPED_TEST_CASE_P(My, FooTest, MyTypes);

To distinguish different instances of the pattern, the first argument to the INSTANTIATE_TYPED_TEST_CASE_P macro is a prefix that will be added to the actual test case name. Remember to pick unique prefixes for different instances.

In the special case where the type list contains only one type, you can write that type directly without ::testing::Types<...>, like this:

INSTANTIATE_TYPED_TEST_CASE_P(My, FooTest, int);

You can see samples/sample6_unittest.cc for a complete example.

Availability: Linux, Windows (requires MSVC 8.0 or above), Mac; since version 1.1.0.

Testing Private Code

If you change your software's internal implementation, your tests should not break as long as the change is not observable by users. Therefore, per the black-box testing principle, most of the time you should test your code through its public interfaces.

If you still find yourself needing to test internal implementation code, consider if there's a better design that wouldn't require you to do so. If you absolutely have to test non-public interface code though, you can. There are two cases to consider:

  • Static functions (not the same as static member functions!) or unnamed namespaces, and
  • Private or protected class members

Static Functions

Both static functions and definitions/declarations in an unnamed namespace are only visible within the same translation unit. To test them, you can #include the entire .cc file being tested in your *_test.cc file. (#including .cc files is not a good way to reuse code - you should not do this in production code!)

However, a better approach is to move the private code into the foo::internal namespace, where foo is the namespace your project normally uses, and put the private declarations in a *-internal.h file. Your production .cc files and your tests are allowed to include this internal header, but your clients are not. This way, you can fully test your internal implementation without leaking it to your clients.

Private Class Members

Private class members are only accessible from within the class or by friends. To access a class' private members, you can declare your test fixture as a friend to the class and define accessors in your fixture. Tests using the fixture can then access the private members of your production class via the accessors in the fixture. Note that even though your fixture is a friend to your production class, your tests are not automatically friends to it, as they are technically defined in sub-classes of the fixture.

Another way to test private members is to refactor them into an implementation class, which is then declared in a *-internal.h file. Your clients aren't allowed to include this header but your tests can. Such is called the Pimpl (Private Implementation) idiom.

Or, you can declare an individual test as a friend of your class by adding this line in the class body:

FRIEND_TEST(TestCaseName, TestName);

For example,

// foo.h
#include "gtest/gtest_prod.h"

// Defines FRIEND_TEST.
class Foo {
  ...
 private:
  FRIEND_TEST(FooTest, BarReturnsZeroOnNull);
  int Bar(void* x);
};

// foo_test.cc
...
TEST(FooTest, BarReturnsZeroOnNull) {
  Foo foo;
  EXPECT_EQ(0, foo.Bar(NULL));
  // Uses Foo's private member Bar().
}

Pay special attention when your class is defined in a namespace, as you should define your test fixtures and tests in the same namespace if you want them to be friends of your class. For example, if the code to be tested looks like:

namespace my_namespace {

class Foo {
  friend class FooTest;
  FRIEND_TEST(FooTest, Bar);
  FRIEND_TEST(FooTest, Baz);
  ...
  definition of the class Foo
  ...
};

}  // namespace my_namespace

Your test code should be something like:

namespace my_namespace {
class FooTest : public ::testing::Test {
 protected:
  ...
};

TEST_F(FooTest, Bar) { ... }
TEST_F(FooTest, Baz) { ... }

}  // namespace my_namespace

Catching Failures

If you are building a testing utility on top of Google Test, you'll want to test your utility. What framework would you use to test it? Google Test, of course.

The challenge is to verify that your testing utility reports failures correctly. In frameworks that report a failure by throwing an exception, you could catch the exception and assert on it. But Google Test doesn't use exceptions, so how do we test that a piece of code generates an expected failure?

"gtest/gtest-spi.h" contains some constructs to do this. After #including this header, you can use

EXPECT_FATAL_FAILURE(statement, substring);

to assert that statement generates a fatal (e.g. ASSERT_*) failure whose message contains the given substring, or use

EXPECT_NONFATAL_FAILURE(statement, substring);

if you are expecting a non-fatal (e.g. EXPECT_*) failure.

For technical reasons, there are some caveats:

  1. You cannot stream a failure message to either macro.
  2. statement in EXPECT_FATAL_FAILURE() cannot reference local non-static variables or non-static members of this object.
  3. statement in EXPECT_FATAL_FAILURE() cannot return a value.

Note: Google Test is designed with threads in mind. Once the synchronization primitives in "gtest/internal/gtest-port.h" have been implemented, Google Test will become thread-safe, meaning that you can then use assertions in multiple threads concurrently. Before

that, however, Google Test only supports single-threaded usage. Once thread-safe, EXPECT_FATAL_FAILURE() and EXPECT_NONFATAL_FAILURE() will capture failures in the current thread only. If statement creates new threads, failures in these threads will be ignored. If you want to capture failures from all threads instead, you should use the following macros:

EXPECT_FATAL_FAILURE_ON_ALL_THREADS(statement, substring);
EXPECT_NONFATAL_FAILURE_ON_ALL_THREADS(statement, substring);

Getting the Current Test's Name

Sometimes a function may need to know the name of the currently running test. For example, you may be using the SetUp() method of your test fixture to set the golden file name based on which test is running. The ::testing::TestInfo class has this information:

namespace testing {

class TestInfo {
 public:
  // Returns the test case name and the test name, respectively.
  //
  // Do NOT delete or free the return value - it's managed by the
  // TestInfo class.
  const char* test_case_name() const;
  const char* name() const;
};

}  // namespace testing
To obtain a TestInfo object for the currently running test, call

current_test_info() on the UnitTest singleton object:

// Gets information about the currently running test.
// Do NOT delete the returned object - it's managed by the UnitTest class.
const ::testing::TestInfo* const test_info =
  ::testing::UnitTest::GetInstance()->current_test_info();
printf("We are in test %s of test case %s.\n",
       test_info->name(), test_info->test_case_name());

current_test_info() returns a null pointer if no test is running. In particular, you cannot find the test case name in TestCaseSetUp(), TestCaseTearDown() (where you know the test case name implicitly), or functions called from them.

Availability: Linux, Windows, Mac.

Extending Google Test by Handling Test Events

Google Test provides an event listener API to let you receive notifications about the progress of a test program and test failures. The events you can listen to include the start and end of the test program, a test case, or a test method, among others. You may use this API to augment or replace the standard console output, replace the XML output, or provide a completely different form of output, such as a GUI or a database. You can also use test events as checkpoints to implement a resource leak checker, for example.

Availability: Linux, Windows, Mac; since v1.4.0.

Defining Event Listeners

To define a event listener, you subclass either testing::TestEventListener or testing::EmptyTestEventListener. The former is an (abstract) interface, where each pure virtual method can be overridden to handle a test event (For example, when a test starts, the OnTestStart() method will be called.). The latter provides an empty implementation of all methods in the interface, such that a subclass only needs to override the methods it cares about.

When an event is fired, its context is passed to the handler function as an argument. The following argument types are used:

  • UnitTest reflects the state of the entire test program,
  • TestCase has information about a test case, which can contain one or more tests,
  • TestInfo contains the state of a test, and
  • TestPartResult represents the result of a test assertion.

An event handler function can examine the argument it receives to find out interesting information about the event and the test program's state. Here's an example:

  class MinimalistPrinter : public ::testing::EmptyTestEventListener {
    // Called before a test starts.
    virtual void OnTestStart(const ::testing::TestInfo& test_info) {
      printf("*** Test %s.%s starting.\n",
             test_info.test_case_name(), test_info.name());
    }

    // Called after a failed assertion or a SUCCEED() invocation.
    virtual void OnTestPartResult(
        const ::testing::TestPartResult& test_part_result) {
      printf("%s in %s:%d\n%s\n",
             test_part_result.failed() ? "*** Failure" : "Success",
             test_part_result.file_name(),
             test_part_result.line_number(),
             test_part_result.summary());
    }

    // Called after a test ends.
    virtual void OnTestEnd(const ::testing::TestInfo& test_info) {
      printf("*** Test %s.%s ending.\n",
             test_info.test_case_name(), test_info.name());
    }
  };

Using Event Listeners

To use the event listener you have defined, add an instance of it to the Google Test event listener list (represented by class TestEventListeners - note the "s" at the end of the name) in your main() function, before calling RUN_ALL_TESTS():

int main(int argc, char** argv) {
  ::testing::InitGoogleTest(&argc, argv);
  // Gets hold of the event listener list.
  ::testing::TestEventListeners& listeners =
      ::testing::UnitTest::GetInstance()->listeners();
  // Adds a listener to the end.  Google Test takes the ownership.
  listeners.Append(new MinimalistPrinter);
  return RUN_ALL_TESTS();
}

There's only one problem: the default test result printer is still in effect, so its output will mingle with the output from your minimalist printer. To suppress the default printer, just release it from the event listener list and delete it. You can do so by adding one line:

  ...
  delete listeners.Release(listeners.default_result_printer());
  listeners.Append(new MinimalistPrinter);
  return RUN_ALL_TESTS();

Now, sit back and enjoy a completely different output from your tests. For more details, you can read this sample.

You may append more than one listener to the list. When an On*Start() or OnTestPartResult() event is fired, the listeners will receive it in the order they appear in the list (since new listeners are added to the end of the list, the default text printer and the default XML generator will receive the event first). An On*End() event will be received by the listeners in the reverse order. This allows output by listeners added later to be framed by output from listeners added earlier.

Generating Failures in Listeners

You may use failure-raising macros (EXPECT_*(), ASSERT_*(), FAIL(), etc) when processing an event. There are some restrictions:

  1. You cannot generate any failure in OnTestPartResult() (otherwise it will cause OnTestPartResult() to be called recursively).
  2. A listener that handles OnTestPartResult() is not allowed to generate any failure.

When you add listeners to the listener list, you should put listeners that handle OnTestPartResult() before listeners that can generate failures. This ensures that failures generated by the latter are attributed to the right test by the former.

We have a sample of failure-raising listener here.

Running Test Programs: Advanced Options

Google Test test programs are ordinary executables. Once built, you can run them directly and affect their behavior via the following environment variables and/or command line flags. For the flags to work, your programs must call ::testing::InitGoogleTest() before calling RUN_ALL_TESTS().

To see a list of supported flags and their usage, please run your test program with the --help flag. You can also use -h, -?, or /? for short. This feature is added in version 1.3.0.

If an option is specified both by an environment variable and by a flag, the latter takes precedence. Most of the options can also be set/read in code: to access the value of command line flag --gtest_foo, write ::testing::GTEST_FLAG(foo). A common pattern is to set the value of a flag before calling ::testing::InitGoogleTest() to change the default value of the flag:

int main(int argc, char** argv) {
  // Disables elapsed time by default.
  ::testing::GTEST_FLAG(print_time) = false;

  // This allows the user to override the flag on the command line.
  ::testing::InitGoogleTest(&argc, argv);

  return RUN_ALL_TESTS();
}

Selecting Tests

This section shows various options for choosing which tests to run.

Listing Test Names

Sometimes it is necessary to list the available tests in a program before running them so that a filter may be applied if needed. Including the flag --gtest_list_tests overrides all other flags and lists tests in the following format:

TestCase1.
  TestName1
  TestName2
TestCase2.
  TestName

None of the tests listed are actually run if the flag is provided. There is no corresponding environment variable for this flag.

Availability: Linux, Windows, Mac.

Running a Subset of the Tests

By default, a Google Test program runs all tests the user has defined. Sometimes, you want to run only a subset of the tests (e.g. for debugging or quickly verifying a change). If you set the GTEST_FILTER environment variable or the --gtest_filter flag to a filter string, Google Test will only run the tests whose full names (in the form of TestCaseName.TestName) match the filter.

The format of a filter is a ':'-separated list of wildcard patterns (called the positive patterns) optionally followed by a '-' and another ':'-separated pattern list (called the negative patterns). A test matches the filter if and only if it matches any of the positive patterns but does not match any of the negative patterns.

A pattern may contain '*' (matches any string) or '?' (matches any single character). For convenience, the filter '*-NegativePatterns' can be also written as '-NegativePatterns'.

For example:

  • ./foo_test Has no flag, and thus runs all its tests.
  • ./foo_test --gtest_filter=* Also runs everything, due to the single match-everything * value.
  • ./foo_test --gtest_filter=FooTest.* Runs everything in test case FooTest.
  • ./foo_test --gtest_filter=*Null*:*Constructor* Runs any test whose full name contains either "Null" or "Constructor".
  • ./foo_test --gtest_filter=-*DeathTest.* Runs all non-death tests.
  • ./foo_test --gtest_filter=FooTest.*-FooTest.Bar Runs everything in test case FooTest except FooTest.Bar.

Availability: Linux, Windows, Mac.

Temporarily Disabling Tests

If you have a broken test that you cannot fix right away, you can add the DISABLED_ prefix to its name. This will exclude it from execution. This is better than commenting out the code or using #if 0, as disabled tests are still compiled (and thus won't rot).

If you need to disable all tests in a test case, you can either add DISABLED_ to the front of the name of each test, or alternatively add it to the front of the test case name.

For example, the following tests won't be run by Google Test, even though they will still be compiled:

// Tests that Foo does Abc.
TEST(FooTest, DISABLED_DoesAbc) { ... }

class DISABLED_BarTest : public ::testing::Test { ... };

// Tests that Bar does Xyz.
TEST_F(DISABLED_BarTest, DoesXyz) { ... }

Note: This feature should only be used for temporary pain-relief. You still have to fix the disabled tests at a later date. As a reminder, Google Test will print a banner warning you if a test program contains any disabled tests.

Tip: You can easily count the number of disabled tests you have using grep. This number can be used as a metric for improving your test quality.

Availability: Linux, Windows, Mac.

Temporarily Enabling Disabled Tests

To include disabled tests in test execution, just invoke the test program with the --gtest_also_run_disabled_tests flag or set the GTEST_ALSO_RUN_DISABLED_TESTS environment variable to a value other than 0. You can combine this with the --gtest_filter flag to further select which disabled tests to run.

Availability: Linux, Windows, Mac; since version 1.3.0.

Repeating the Tests

Once in a while you'll run into a test whose result is hit-or-miss. Perhaps it will fail only 1% of the time, making it rather hard to reproduce the bug under a debugger. This can be a major source of frustration.

The --gtest_repeat flag allows you to repeat all (or selected) test methods in a program many times. Hopefully, a flaky test will eventually fail and give you a chance to debug. Here's how to use it:

$ foo_test --gtest_repeat=1000 Repeat foo_test 1000 times and don't stop at failures.
$ foo_test --gtest_repeat=-1 A negative count means repeating forever.
$ foo_test --gtest_repeat=1000 --gtest_break_on_failure Repeat foo_test 1000 times, stopping at the first failure. This is especially useful when running under a debugger: when the testfails, it will drop into the debugger and you can then inspect variables and stacks.
$ foo_test --gtest_repeat=1000 --gtest_filter=FooBar Repeat the tests whose name matches the filter 1000 times.

If your test program contains global set-up/tear-down code registered using AddGlobalTestEnvironment(), it will be repeated in each iteration as well, as the flakiness may be in it. You can also specify the repeat count by setting the GTEST_REPEAT environment variable.

Availability: Linux, Windows, Mac.

Shuffling the Tests

You can specify the --gtest_shuffle flag (or set the GTEST_SHUFFLE environment variable to 1) to run the tests in a program in a random order. This helps to reveal bad dependencies between tests.

By default, Google Test uses a random seed calculated from the current time. Therefore you'll get a different order every time. The console output includes the random seed value, such that you can reproduce an order-related test failure later. To specify the random seed explicitly, use the --gtest_random_seed=SEED flag (or set the GTEST_RANDOM_SEED environment variable), where SEED is an integer between 0 and 99999. The seed value 0 is special: it tells Google Test to do the default behavior of calculating the seed from the current time.

If you combine this with --gtest_repeat=N, Google Test will pick a different random seed and re-shuffle the tests in each iteration.

Availability: Linux, Windows, Mac; since v1.4.0.

Controlling Test Output

This section teaches how to tweak the way test results are reported.

Colored Terminal Output

Google Test can use colors in its terminal output to make it easier to spot the separation between tests, and whether tests passed.

You can set the GTEST_COLOR environment variable or set the --gtest_color command line flag to yes, no, or auto (the default) to enable colors, disable colors, or let Google Test decide. When the value is auto, Google Test will use colors if and only if the output goes to a terminal and (on non-Windows platforms) the TERM environment variable is set to xterm or xterm-color.

Availability: Linux, Windows, Mac.

Suppressing the Elapsed Time

By default, Google Test prints the time it takes to run each test. To suppress that, run the test program with the --gtest_print_time=0 command line flag. Setting the GTEST_PRINT_TIME environment variable to 0 has the same effect.

Availability: Linux, Windows, Mac. (In Google Test 1.3.0 and lower, the default behavior is that the elapsed time is not printed.)

Generating an XML Report

Google Test can emit a detailed XML report to a file in addition to its normal textual output. The report contains the duration of each test, and thus can help you identify slow tests.

To generate the XML report, set the GTEST_OUTPUT environment variable or the --gtest_output flag to the string "xml:_path_to_output_file_", which will create the file at the given location. You can also just use the string "xml", in which case the output can be found in the test_detail.xml file in the current directory.

If you specify a directory (for example, "xml:output/directory/" on Linux or "xml:output\directory\" on Windows), Google Test will create the XML file in that directory, named after the test executable (e.g. foo_test.xml for test program foo_test or foo_test.exe). If the file already exists (perhaps left over from a previous run), Google Test will pick a different name (e.g. foo_test_1.xml) to avoid overwriting it.

The report uses the format described here. It is based on the junitreport Ant task and can be parsed by popular continuous build systems like Hudson. Since that format was originally intended for Java, a little interpretation is required to make it apply to Google Test tests, as shown here:

<testsuites name="AllTests" ...>
  <testsuite name="test_case_name" ...>
    <testcase name="test_name" ...>
      <failure message="..."/>
      <failure message="..."/>
      <failure message="..."/>
    </testcase>
  </testsuite>
</testsuites>
  • The root <testsuites> element corresponds to the entire test program.
  • <testsuite> elements correspond to Google Test test cases.
  • <testcase> elements correspond to Google Test test functions.

For instance, the following program

TEST(MathTest, Addition) { ... }
TEST(MathTest, Subtraction) { ... }
TEST(LogicTest, NonContradiction) { ... }

could generate this report:

<?xml version="1.0" encoding="UTF-8"?>
<testsuites tests="3" failures="1" errors="0" time="35" name="AllTests">
  <testsuite name="MathTest" tests="2" failures="1" errors="0" time="15">
    <testcase name="Addition" status="run" time="7" classname="">
      <failure message="Value of: add(1, 1)&#x0A; Actual: 3&#x0A;Expected: 2" type=""/>
      <failure message="Value of: add(1, -1)&#x0A; Actual: 1&#x0A;Expected: 0" type=""/>
    </testcase>
    <testcase name="Subtraction" status="run" time="5" classname="">
    </testcase>
  </testsuite>
  <testsuite name="LogicTest" tests="1" failures="0" errors="0" time="5">
    <testcase name="NonContradiction" status="run" time="5" classname="">
    </testcase>
  </testsuite>
</testsuites>

Things to note:

  • The tests attribute of a <testsuites> or <testsuite> element tells how many test functions the Google Test program or test case contains, while the failures attribute tells how many of them failed.
  • The time attribute expresses the duration of the test, test case, or entire test program in milliseconds.
  • Each <failure> element corresponds to a single failed Google Test assertion.
  • Some JUnit concepts don't apply to Google Test, yet we have to conform to the DTD. Therefore you'll see some dummy elements and attributes in the report. You can safely ignore these parts.

Availability: Linux, Windows, Mac.

Controlling How Failures Are Reported

Turning Assertion Failures into Break-Points

When running test programs under a debugger, it's very convenient if the debugger can catch an assertion failure and automatically drop into interactive mode. Google Test's break-on-failure mode supports this behavior.

To enable it, set the GTEST_BREAK_ON_FAILURE environment variable to a value other than 0 . Alternatively, you can use the --gtest_break_on_failure command line flag.

Availability: Linux, Windows, Mac.

Disabling Catching Test-Thrown Exceptions

Google Test can be used either with or without exceptions enabled. If a test throws a C++ exception or (on Windows) a structured exception (SEH), by default Google Test catches it, reports it as a test failure, and continues with the next test method. This maximizes the coverage of a test run. Also, on Windows an uncaught exception will cause a pop-up window, so catching the exceptions allows you to run the tests automatically.

When debugging the test failures, however, you may instead want the exceptions to be handled by the debugger, such that you can examine the call stack when an exception is thrown. To achieve that, set the GTEST_CATCH_EXCEPTIONS environment variable to 0, or use the --gtest_catch_exceptions=0 flag when running the tests.

Availability: Linux, Windows, Mac.

Letting Another Testing Framework Drive

If you work on a project that has already been using another testing framework and is not ready to completely switch to Google Test yet, you can get much of Google Test's benefit by using its assertions in your existing tests. Just change your main() function to look like:

#include "gtest/gtest.h"

int main(int argc, char** argv) {
  ::testing::GTEST_FLAG(throw_on_failure) = true;
  // Important: Google Test must be initialized.
  ::testing::InitGoogleTest(&argc, argv);

  ... whatever your existing testing framework requires ...
}

With that, you can use Google Test assertions in addition to the native assertions your testing framework provides, for example:

void TestFooDoesBar() {
  Foo foo;
  EXPECT_LE(foo.Bar(1), 100);     // A Google Test assertion.
  CPPUNIT_ASSERT(foo.IsEmpty());  // A native assertion.
}

If a Google Test assertion fails, it will print an error message and throw an exception, which will be treated as a failure by your host testing framework. If you compile your code with exceptions disabled, a failed Google Test assertion will instead exit your program with a non-zero code, which will also signal a test failure to your test runner.

If you don't write ::testing::GTEST_FLAG(throw_on_failure) = true; in your main(), you can alternatively enable this feature by specifying the --gtest_throw_on_failure flag on the command-line or setting the GTEST_THROW_ON_FAILURE environment variable to a non-zero value.

Death tests are not supported when other test framework is used to organize tests.

Availability: Linux, Windows, Mac; since v1.3.0.

Distributing Test Functions to Multiple Machines

If you have more than one machine you can use to run a test program, you might want to run the test functions in parallel and get the result faster. We call this technique sharding, where each machine is called a shard.

Google Test is compatible with test sharding. To take advantage of this feature, your test runner (not part of Google Test) needs to do the following:

  1. Allocate a number of machines (shards) to run the tests.
  2. On each shard, set the GTEST_TOTAL_SHARDS environment variable to the total number of shards. It must be the same for all shards.
  3. On each shard, set the GTEST_SHARD_INDEX environment variable to the index of the shard. Different shards must be assigned different indices, which must be in the range [0, GTEST_TOTAL_SHARDS - 1].
  4. Run the same test program on all shards. When Google Test sees the above two environment variables, it will select a subset of the test functions to run. Across all shards, each test function in the program will be run exactly once.
  5. Wait for all shards to finish, then collect and report the results.

Your project may have tests that were written without Google Test and thus don't understand this protocol. In order for your test runner to figure out which test supports sharding, it can set the environment variable GTEST_SHARD_STATUS_FILE to a non-existent file path. If a test program supports sharding, it will create this file to acknowledge the fact (the actual contents of the file are not important at this time; although we may stick some useful information in it in the future.); otherwise it will not create it.

Here's an example to make it clear. Suppose you have a test program foo_test that contains the following 5 test functions:

TEST(A, V)
TEST(A, W)
TEST(B, X)
TEST(B, Y)
TEST(B, Z)

and you have 3 machines at your disposal. To run the test functions in parallel, you would set GTEST_TOTAL_SHARDS to 3 on all machines, and set GTEST_SHARD_INDEX to 0, 1, and 2 on the machines respectively. Then you would run the same foo_test on each machine.

Google Test reserves the right to change how the work is distributed across the shards, but here's one possible scenario:

  • Machine #0 runs A.V and B.X.
  • Machine #1 runs A.W and B.Y.
  • Machine #2 runs B.Z.

Availability: Linux, Windows, Mac; since version 1.3.0.

Fusing Google Test Source Files

Google Test's implementation consists of ~30 files (excluding its own tests). Sometimes you may want them to be packaged up in two files (a .h and a .cc) instead, such that you can easily copy them to a new machine and start hacking there. For this we provide an experimental Python script fuse_gtest_files.py in the scripts/ directory (since release 1.3.0). Assuming you have Python 2.4 or above installed on your machine, just go to that directory and run

python fuse_gtest_files.py OUTPUT_DIR

and you should see an OUTPUT_DIR directory being created with files gtest/gtest.h and gtest/gtest-all.cc in it. These files contain everything you need to use Google Test. Just copy them to anywhere you want and you are ready to write tests. You can use the scripts/test/Makefile file as an example on how to compile your tests against them.

Where to Go from Here

Congratulations! You've now learned more advanced Google Test tools and are ready to tackle more complex testing tasks. If you want to dive even deeper, you can read the Frequently-Asked Questions.

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