public TopicName createTopicWithoutPrefix(String topicName) {
    checkArgument(!topicName.isEmpty(), "topicName can not be empty");
    checkIsUsable();

    TopicName name = TopicName.of(projectId, topicName);
    return createTopicInternal(name);
  }
@Test
  public void testCreateTopicWithoutPrefixWithInvalidNameShouldFail() {
    IllegalArgumentException exception =
        assertThrows(
            IllegalArgumentException.class, () -> testManager.createTopicWithoutPrefix(""));
    assertThat(exception).hasMessageThat().contains("topicName can not be empty");
  }