By this it is also possible to add user provided code as an input, e.g. by annotating an `@link:{javadocPath}/org/gradle/api/Action.html[Action]` property with `@link:{javadocPath}/org/gradle/api/tasks/Nested.html[Nested]`.
Note that any inputs to such actions should be tracked, either by annotated properties on the action or by manually registering them with the task.

	fakeCMClient := &cmfake.FakeCustomMetricsClient{}
	fakeCMClient.AddReactor("get", "*", func(action core.Action) (handled bool, ret runtime.Object, err error) {
		getForAction, wasGetFor := action.(cmfake.GetForAction)
		if !wasGetFor {
			return true, nil, fmt.Errorf("expected a get-for action, got %v instead", action)
		}

		if tc.metric == nil {
			return true, nil, fmt.Errorf("no custom metrics specified in test client")

	}
}

func createListReactor(tracker cgotesting.ObjectTracker, kind string) func(action cgotesting.Action) (handled bool, ret apiruntime.Object, err error) {
	return func(action cgotesting.Action) (handled bool, ret apiruntime.Object, err error) {
		// listAction := action.(cgotesting.ListAction)
		gvr := action.GetResource()
		ns := action.GetNamespace()
		gvr.Resource += "es"

        description                 | mutation
        "outputs.cacheIf { false }" | "outputs.cacheIf { false }"
        "eachFile(Closure)"         | "eachFile {}"
        "eachFile(Action)"          | "eachFile(org.gradle.internal.Actions.doNothing())"
        "expand(Map)"               | "expand([:])"
        "filter(Closure)"           | "filter {}"
        "filter(Class)"             | "filter(PushbackReader)"

=== Deprecations

[[java_lamdba_action]]
==== Using Java lambdas as task actions

When using a Java lambda to implement a task action, Gradle cannot track the implementation and the task will never be up-to-date or served from the build cache.
Since it is easy to add such a task action, using task actions implemented by Java lambdas is now deprecated.

 * You can no longer cast `FileCollection` objects to other types using the `as` keyword or the `asType()` method.
 * You can no longer pass `null` as the configuration action of link:{javadocPath}/org/gradle/api/file/CopySpec.html#from-java.lang.Object-org.gradle.api.Action-[CopySpec.from(Object, Action)].

	// the first non-empty line that is not a build constraint.
	var action string
	for actionSrc := src; action == "" && actionSrc != ""; {
		var line string
		line, actionSrc, _ = strings.Cut(actionSrc, "\n")
		if constraint.IsGoBuild(line) || constraint.IsPlusBuild(line) {
			continue
		}
		action = strings.TrimSpace(strings.TrimPrefix(line, "//"))
	}
	if action == "" {

	//
	// Failures defined by the ValidatingAdmissionPolicy's FailurePolicy are enforced according
	// to these actions only if the FailurePolicy is set to Fail, otherwise the failures are
	// ignored. This includes compilation errors, runtime errors and misconfigurations of the policy.
	//
	// validationActions is declared as a set of action values. Order does

                return factory.create().length()
            }

            @Provides
            Factory<String> createString(Callable<String> action) {
                return { action.call() } as Factory
            }

            @Provides
            Callable<String> createAction() {
                return { "hi" }
            }
        })

        expect:

			PathSeparatedPrefix: "/route/v1",
		}))
		g.Expect(routes[0].Action.(*envoyroute.Route_Route).Route.ClusterNotFoundResponseCode).
			To(Equal(envoyroute.RouteAction_INTERNAL_SERVER_ERROR))
		g.Expect(routes[1].Match.PathSpecifier).To(Equal(&envoyroute.RouteMatch_Prefix{
			Prefix: "/",
		}))
		g.Expect(routes[1].Action.(*envoyroute.Route_Route).Route.ClusterNotFoundResponseCode).