public static Matcher<Map<String, String>> equalOnKeysOf(Map<String, String> expected) {
    return new TypeSafeMatcher<Map<String, String>>() {

      @Override
      public void describeTo(Description description) {
        description.appendText("map equal on keys: ").appendValue(expected);
      }

      @Override
      protected boolean matchesSafely(Map<String, String> actual) {
        Set<String> keys = expected.keySet();
        actual.keySet().retainAll(keys);

        return actual.equals(expected);
      }
    };
  }