@Test
public void keySet() throws Exception {

    multiMap.putAll(ImmutableListMultimap.of(
            "first", new TestEntity("1", "v1"),
            "second", new TestEntity("2", "v2"),
            "second", new TestEntity("3", "v3")
    ));
    assertThat(multiMap.keySet()).containsExactly("first", "second");
}