In hamcrest-java there are matchers IsEmptyCollection, IsCollectionWithSize.

I would like a similar pair to be implemented for java.util.Map, i.e. IsEmptyMap, IsMapWithSize.

A goal is to be able to test that a map is null or empty, like the following: anyOf(nullValue(),emptyMap())

The Map contract defines that maps (of any concrete type) can be compared for equality. So, isEmptyMap() is the same as equalTo(emptyMap()), where emptyMap is imported from java.util.Collections

IsMapWithSize is a reasonable matcher.

If I understand, you're saying that IsEmptyMap shouldn't be a class, because there is a significant difference between the Map contract and the Collection contract. While the "empty map" method can be implemented trivially, the "empty collections" contract can't be trivially implemented because Collections encompass things like Lists, Sets, and Queues, which can't be compared to a "generic empty instance" in the same way maps can.

Despite this, it would still be a nice to have an "emptyMap()" utility method on org.hamcrest.Matchers. This utility method may just be a "one line method" but it's a pretty ugly method:

public static Matcher> emptyMap() { return describedAs("an empty map", equalTo(Collections. emptyMap())); }

There's my best attempt; I've probably screwed it up myself, here, as I tend to take a trial-and-error approach with generics.

As an afterthought; it seems like IsEmptyCollection and IsEmptyMap can each be implemented trivially as derivations of IsCollectionWithSize and IsMapWithSize. I'm not sure if this approach is realistic, but it seems like it could cut down on "class clutter" and solve this problem in a somewhat elegant/symmetrical way.

The idea of comparing the map (as mapping) using equality is good, but I think that the issue is more related with the consistency and ease of use of the Hamcrest API, which would benefit from adding this simple method. Thanks for the alternative solution.

tagging

I have added some new map size matchers in the following commit: https://github.com/hamcrest/JavaHamcrest/commit/749ef4be528e489139aec9d5ad40188078dab389

This should give you access to: is(aMapWithSize(3)) is(aMapWithSize(equalTo(3))) is(anEmptyMap())

Backport to the hamcrest-java-gwt branch