java.util.Map is not a subtype of java.util.Collection

Please provide a way to match on its size.

Comment deleted

You have my permission to incorporate the source into your code base without mentioning my name if necessary.

You can achieve this using the existing matchers by using the map's entry set.

    final Map<String, String> map = new HashMap<String, String>();

    MatcherAssert.assertThat(map.entrySet(), Matchers.hasSize(3));

Oh, and such a Matcher has already been written for inclusion in the next release of Hamcrest -- see https://github.com/hamcrest/JavaHamcrest/blob/master/hamcrest-library/src/main/java/org/hamcrest/collection/IsMapWithSize.java

When this is released, you'll be able to do:

    MatcherAssert.assertThat(map, Matchers.aMapWithSize(3));