This comment was originally written by @sethladd

File under Area=UnitTest

Removed Type-Defect label.
Added Type-Enhancement, Area-UnitTest, Triaged labels.

This comment was originally written by @seaneagan

For starters could make most Iterable Matchers also work for Streams, since the API is so similar:

isEmpty
hasLength
contains
isIn
orderedEquals
unorderedEquals
someElement (rename to anyElement, since Iterable.some is now Iterable.any)
everyElement

This comment was originally written by @seaneagan

I think to help with implementing these sorts of Matchers, it would probably be useful if Matcher.matches were allowed to return a Future<bool> instead of just a bool.

This comment was originally written by @seaneagan

And actually it would probably work better as a rich MatchResult object instead of a plain bool, so it can store data about why it didn't match, to be used in "describe":

class Matcher {
  /// returns either [MatchResult] or [Future<MatchResult>] representing the match result
  match(object);
}

class MatchResult {
  final bool isMatch;
  Description describe(Description description, {bool verbose = false});
}
class Match extends MatchResult {...}
class Mismatch extends MatchResult {...}

Regarding the mismatch state, we already have a mechanism for that (MatchState).

This comment was originally written by @seaneagan

returning Future<bool> from Matcher.matches is filed as issue #10188

Added Pkg-Unittest label.

Removed Area-UnitTest label.
Added Area-Pkg label.

Removed Pkg-Unittest label.
Added Pkg-matcher label.

cc @kevmoo @nex3

Please close if this isn't planned.

This is still planned, although it'll be in test rather than matcher.

This issue was moved to dart-lang/test#134

This issue has been moved to dart-lang/matcher#13.