@Test
  public void testGiant31() {
    Giant31.Builder builder = Giant31.builder();
    builder.setFirst30();
    builder.x31(31);
    Giant31 giant = builder.build();
    assertThat(giant.x1()).isEqualTo(1);
    assertThat(giant.x31()).isEqualTo(31);

    builder = Giant31.builder();
    builder.setFirst30();
    try {
      builder.build();
      fail();
    } catch (IllegalStateException expected) {
      if (omitIdentifiers) {
        assertThat(expected).hasMessageThat().isNull();
      } else {
        assertThat(expected).hasMessageThat().contains("x31");
        assertThat(expected).hasMessageThat().doesNotContain("x30");
      }
    }
  }
Notice that this is called ReleaseInfoBuilder and not Builder.
value/src/it/functional/src/test/java/com/google/auto/value/AutoValueTest.java