public static Builder builder() {
    return new Builder();
  }
@Test
  public void testBuilder_fail() {
    try {
      CachedLayer.builder().build();
      Assert.fail("missing required");

    } catch (NullPointerException ex) {
      MatcherAssert.assertThat(ex.getMessage(), CoreMatchers.containsString("layerDigest"));
    }

    try {
      CachedLayer.builder().setLayerDigest(mockLayerDigest).build();
      Assert.fail("missing required");

    } catch (NullPointerException ex) {
      MatcherAssert.assertThat(ex.getMessage(), CoreMatchers.containsString("layerDiffId"));
    }

    try {
      CachedLayer.builder().setLayerDigest(mockLayerDigest).setLayerDiffId(mockLayerDiffId).build();
      Assert.fail("missing required");

    } catch (NullPointerException ex) {
      MatcherAssert.assertThat(ex.getMessage(), CoreMatchers.containsString("layerBlob"));
    }
  }