[FIXED] Match List of objects against list of properties

Issue

I'm trying to use hamcrest matchers to match a list of objects against a list/array of their properties. For one property value this is not a problem, because I can do something like this:

assertThat(savedGroup.getMembers(),
    containsInAnyOrder(hasProperty("name", is(NAMES[0]))));

For multiple property values I can use multiple hasProperty() calls

assertThat(savedGroup.getMembers(),
    containsInAnyOrder(
        hasProperty("name", is(NAMES[0])),
        hasProperty("name", is(NAMES[1]))));

But is there a generic way to match against all values in the NAMES array?

Solution

The best way (IMO) to do this would be to combine the overloaded containsInAnyOrder Matcher along with a custom FeatureMatcher. Ultimately your code would look like this:

String[] expectedNames = new String[] { "John", "Bob", "Carol"};
assertThat(savedGroup.getMembers(), hasNames(expectedNames));

hasNames is implemented as follows:

private Matcher<Iterable<? extends Member>> hasNames(String[] expectedNames) {
    return containsInAnyOrder(Arrays.stream(expectedNames).map(name -> name(name)).collect(Collectors.toList()));
}

And the final part is the call to name which generates a Matcher that will extract a property in a type-safe way from your object:

private Matcher<Member> name(String name) {
    return new FeatureMatcher<Member, String>(equalTo(name), "name", "name") {
        @Override
        protected String featureValueOf(Member actual) {
            return actual.getName();
        }
    };
}

The benefit of doing it this is way is that:

• You get the benefit of type-safety instead of using hasProperty
• Your test now describes what you actual want to match on, i.e. hasNames
• The code produced is now more flexible and composable. Want to match a single objects name? All you now need to do is assertThat(member, has(name("Fred")))

You can get even more composability by moving the equalTo sub-matcher to be part of the hasNames call like this:

private Matcher<Iterable<? extends Member>> hasNames(String[] expectedNames) {
    return containsInAnyOrder(Arrays.stream(expectedNames).map(name -> name(equalTo(name))).collect(Collectors.toList()));
}

private Matcher<Member> name(Matcher<String> nameMatcher) {
    return new FeatureMatcher<Member, String>(nameMatcher, "name", "name") {
        @Override
        protected String featureValueOf(Member actual) {
            return actual.getName();
        }
    };
}

Answered By - tddmonkey
Answer Checked By - Clifford M. (JavaFixing Volunteer)