@Test
  public void testGiant33() {
    Giant33.Builder builder = Giant33.builder();
    builder.setFirst30();
    builder.x31(31);
    builder.x32(32);
    builder.x33(33);
    Giant33 giant = builder.build();
    assertThat(giant.x1()).isEqualTo(1);
    assertThat(giant.x31()).isEqualTo(31);
    assertThat(giant.x32()).isEqualTo(32);
    assertThat(giant.x33()).isEqualTo(33);

    builder = Giant33.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().contains("x32");
        assertThat(expected).hasMessageThat().contains("x33");
        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