@Test
    public void testGetOrCreateListValue() {
        Map<String, List<String>> map = new HashMap<>();
        List<String> fooList = KafkaAdminClient.getOrCreateListValue(map, "foo");
        assertNotNull(fooList);
        fooList.add("a");
        fooList.add("b");
        List<String> fooList2 = KafkaAdminClient.getOrCreateListValue(map, "foo");
        assertEquals(fooList, fooList2);
        assertTrue(fooList2.contains("a"));
        assertTrue(fooList2.contains("b"));
        List<String> barList = KafkaAdminClient.getOrCreateListValue(map, "bar");
        assertNotNull(barList);
        assertTrue(barList.isEmpty());
    }
A unit test for KafkaAdminClient.

See AdminClientIntegrationTest for an integration test.
clients/src/test/java/org/apache/kafka/clients/admin/KafkaAdminClientTest.java