@Test
    public void testMultipleCollectionsWithoutDuplicates() throws Exception
    {
        // Setup test fixture.
        final List<String> input1 = Arrays.asList("a", "b");
        final List<String> input2 = Arrays.asList("c", "d");
        final List<String> input3 = Arrays.asList("e", "f", "g");

        // Execute system under test.
        @SuppressWarnings("unchecked")
        final Set<String> result = CollectionUtils.findDuplicates(input1, input2, input3);

        // Verify results.
        assertTrue(result.isEmpty());
    }
Verifies that {@link CollectionUtils#findDuplicates(Collection[])} finds duplicates when the provided
collections have some.
xmppserver/src/test/java/org/jivesoftware/util/CollectionUtilsTest.java