@Test
  public void source9_masked() throws Exception {
    assumeTrue(isJdk9OrLater());
    String generated =
        runProcessor(
            ImmutableList.of("-source", "9", "-target", "9"), "javax.annotation.processing");
    assertThat(generated).doesNotContain(JAVAX_ANNOTATION_GENERATED);
    assertThat(generated).doesNotContain(JAVAX_ANNOTATION_PROCESSING_GENERATED);
  }
Used to produce a {@link StandardJavaFileManager} where a certain package appears to have no
classes. The results are exactly those from the proxied {@code StandardJavaFileManager} except
for the {@link StandardJavaFileManager#list list} method when its {@code packageName} argument
is the given package, in which case the result is an empty list.

<p>We can't use {@link javax.tools.ForwardingJavaFileManager} because at least some JDK
versions require the file manager to be a {@code StandardJavaFileManager} when the {@code
--release} flag is given.
common/src/test/java/com/google/auto/common/GeneratedAnnotationsTest.java