How to assert that a list has at least n items which are greater than x (with hamcrest in junit)

Question

I could with following code check if a list has a item, which greater than 30.

//Using Hamcrest
List ints= Arrays.asList(22,33,44,55);
assertT         


        

Answer 1

You can create your own specific matcher, like:

class ListMatcher {
  public static Matcher> hasAtLeastItemsGreaterThan(final int targetCount, final int lowerLimit) {
    return new TypeSafeMatcher>() {

        @Override
        public void describeTo(final Description description) {
            description.appendText("should have at least " + targetCount + " items greater than " + lowerLimit);
        }

        @Override
        public void describeMismatchSafely(final List arg0, final Description mismatchDescription) {
            mismatchDescription.appendText("was ").appendValue(arg0.toString());
        }

        @Override
        protected boolean matchesSafely(List values) {
            int actualCount = 0;
            for (int value : values) {
                if (value > lowerLimit) {
                    actualCount++;
                }

            }
            return actualCount >= targetCount;
        }
    };
}
}

And then use it like:

public class ListMatcherTests {

@Test
public void testListMatcherPasses() {
    List underTest = Arrays.asList(1, 10, 20);
    assertThat(underTest, ListMatcher.hasAtLeastItemsGreaterThan(2, 5));
}

@Test
public void testListMatcherFails() {
    List underTest = Arrays.asList(1, 10, 20);
    assertThat(underTest, ListMatcher.hasAtLeastItemsGreaterThan(2, 15));
}

Of course, this is a bit of work; and not very generic. But it works.

Alternatively, you could simply "iterate" your list within your specific test method.