@Test
  public void testRunPluginExtensions_configuredExtensionNotFound() {
    try {
      gradleProjectProperties.runPluginExtensions(
          Arrays.asList(new FooExtensionConfig()), containerBuilder);
      Assert.fail();
    } catch (JibPluginExtensionException ex) {
      Assert.assertEquals(
          "extension configured but not discovered on Jib runtime classpath: com.google.cloud."
              + "tools.jib.gradle.GradleProjectPropertiesExtensionTest$FooExtension",
          ex.getMessage());
    }
  }
Plugin extension test for {@link GradleProjectProperties}.
jib-gradle-plugin/src/test/java/com/google/cloud/tools/jib/gradle/GradleProjectPropertiesExtensionTest.java