Question

The answer to this old question recommends Hamcrest for asserting on collections.

What happens if I want to assert a collection has multiple instances of an object?

list = newArrayList();
list.add(1);
list.add(1);
list.add(2);
assertThat(list, hasItems(1, 2, 2)); // This should fail
assertThat(list, hasItems(1, 2, 1)); // This should pass

The hamcrest code I tried does not care about multiplicity – both asserts above will pass.

Answer 1

The easiest technique I can think of is sorting the list first and then using equality comparison:

Collections.sort(list);

And then:

assertEquals(Arrays.asList(1, 1, 2), list);