@Test
  void singleElementIn() {
    check(criteria.value.in(Collections.singleton("v1"))).matches("{value: 'v1'}");
    check(criteria.value.notIn(Collections.singleton("v1"))).matches("{value: {$ne: 'v1'}}");
  }
{@code in} / {@code notIn} with single element converted to {@code eq} / {@code ne}
criteria/mongo/test/org/immutables/criteria/mongo/FindVisitorTest.java