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javajunitjava-8junit4assertj

Assert list contains exactly one element satisfying condition

In my JUnit test I want to assert that a list contains exactly one element satisfying a given condition (there can be many elements in the list, but only one should satisfy the condition). I wrote the code below, but I was wondering if it's possible to get rid of the "new Condition<>"-part and use a "pure" lambda? Or are there other, more elegant ways to accomplish what I am trying to do?

class Foo {
  String u;

  Foo(String u) { this.u = u; }

  String getIt() { return u; }
}

@Test
public void testIt() {
  List<Foo> list = Lists.newArrayList(new Foo("abc"), new Foo("xyz"));

  assertThat(list)
        .haveExactly(1, new Condition<>(
                x -> "xyz".equals(x.getIt()),
                "Fail"));
}
Solution

  • This should work (but I haven't tested it):

    assertThat(list).extracting(Foo::getIt)
                .containsOnlyOnce("xyz");