Add undocumented action duration method

src/Actions.js

@@ -1,4 +1,5 @@
 import stampit from 'stampit';
+import warning from 'warning';
 import debugFactory from 'debug';
 import {
   Observable,
@@ -10,6 +11,7 @@ import {
 
 import waitFor from './waitFor';
 
+const __DEV__ = process.env.NODE_ENV !== 'production';
 const { checkDisposed } = Disposable;
 const assign = Object.assign;
 const debug = debugFactory('thundercats:actions');
@@ -50,6 +52,7 @@ export function create(shouldBind, { name, map }) {
   const observers = [];
   const actionDisposable = new CompositeDisposable();
   const actionStart = new Subject();
+  const actionEnd = new Subject();
   const maybeBound = shouldBind ?
     map.bind(this) :
     map;
@@ -81,6 +84,9 @@ export function create(shouldBind, { name, map }) {
       .doOnNext(
         value => observers.forEach(observer => observer.onNext(value))
       )
+      .doOnCompleted(
+        () => actionEnd.onNext()
+      )
       .subscribe(
         () => debug('%s onNext', name),
         err => {
@@ -123,10 +129,25 @@ export function create(shouldBind, { name, map }) {
   };
 
   action.waitFor = function() {
+    /* istanbul ignore else */
+    if (__DEV__) {
+      warning(
+        false,
+        'action.waitFor is deprecated and will be removed in ' +
+        'the next version of thundercats'
+      );
+    }
     return actionStart
       .flatMap(payload => waitFor(...arguments).map(() => payload));
   };
 
+  // NOTE: not public API. May change or be removed at any time
+  action.__duration = function __duration() {
+    return actionStart
+      .flatMap(actionEnd)
+      .first();
+  };
+
   action._subscribe = function subscribeToAction(observer) {
     // in next major version this should check if action
     // has been stopped or disposed and act accordingly

test/action.js

@@ -275,6 +275,41 @@ describe('Actions', function() {
     });
   });
 
+  describe('internal lifecycle hooks', function() {
+    it('should have a duration observable', () => {
+      const catActions = Actions({ purr: null })();
+      assert(
+        !!catActions.purr.__duration,
+        'actions should have a __durations property'
+      );
+    });
+
+    it('should on call __duration once per action', () => {
+      const spy = sinon.spy();
+      const spy2 = sinon.spy();
+      const catActions = Actions({ purr: null })();
+      catActions.purr.__duration().subscribe(spy);
+      catActions.purr(Observable.of(1, 2, 3));
+      assert(
+        spy.calledOnce,
+        'duration Observer was called more than once'
+      );
+
+      catActions.purr.__duration().subscribe(spy2);
+      catActions.purr(Observable.of(1, 2, 3));
+
+      assert(
+        spy.calledOnce,
+        'duration Observable spy was called more than once'
+      );
+
+      assert(
+        spy2.calledOnce,
+        'duration Observable spy was called more than once'
+      );
+    });
+  });
+
   describe('disposal', function() {
     let catActions;