@Test
public void testJoinSets() {
AssertExtensions.<Integer>assertContainsSameElements("Empty set.", Collections.emptySet(),
CollectionHelpers.joinSets(Collections.emptySet(), Collections.emptySet()));
AssertExtensions.assertContainsSameElements("Empty+non-empty.", Sets.newHashSet(1, 2, 3),
CollectionHelpers.joinSets(Collections.emptySet(), Sets.newHashSet(1, 2, 3)));
AssertExtensions.assertContainsSameElements("Non-empty+empty.", Sets.newHashSet(1, 2, 3),
CollectionHelpers.joinSets(Sets.newHashSet(1, 2, 3), Collections.emptySet()));
AssertExtensions.assertContainsSameElements("Non-empty+non-empty.", Sets.newHashSet(1, 2, 3),
CollectionHelpers.joinSets(Sets.newHashSet(1, 3), Sets.newHashSet(2)));
AssertExtensions.assertContainsSameElements("Non-empty+non-empty(duplicates).", Arrays.asList(1, 2, 2, 3),
CollectionHelpers.joinSets(Sets.newHashSet(1, 2), Sets.newHashSet(2, 3)));
}