Expose effectMetadata() useful in testing

This PR exposes a method to get metadata supplied
through @effect() decorator.

This method is useful for when we want to test
that an effect was properly decorated/registered
in the store.

Related issue: ngrx#491

docs/effects/testing.md

@@ -47,6 +47,46 @@ describe('My Effects', () => {
     effects.someSource$.subscribe(result => {
       expect(result).toEqual(AnotherAction);
     });
-  });  
+  });
+});
+```
+
+### effectMetadata
+Returns decorator configuration for an effect in an instance of effects.
+Use this function to ensure that an effect has been properly decorated.
+
+If the decorator was not supplied, the result is `undefined`.
+
+Usage:
+```ts
+import { TestBed } from '@angular/core/testing';
+import { effectMetadata } from '@ngrx/effects';
+import { MyEffects } from './my-effects';
+
+describe('My Effects', () => {
+  let effects: MyEffects;
+
+  beforeEach(() => {
+    TestBed.configureTestingModule({
+      providers: [
+        MyEffects,
+        // other providers
+      ],
+    });
+
+    effects = TestBed.get(MyEffects);
+  });
+
+  it('should register someSource$', () => {
+    expect(effectMetadata(effects, 'someSource$')).toEqual({
+      dispatch: true,
+    });
+  });
+
+  it('should register someOtherSource$', () => {
+    expect(effectMetadata(effects, 'someOtherSource$')).toEqual({
+      dispatch: false,
+    });
+  });
 });
 ```

modules/effects/spec/effects_metadata.spec.ts

@@ -1,5 +1,6 @@
 import {
   Effect,
+  effectMetadata,
   getSourceMetadata,
   getSourceForInstance,
 } from '../src/effects_metadata';
@@ -46,4 +47,32 @@ describe('Effect Metadata', () => {
       expect(proto).toBe(Fixture.prototype);
     });
   });
+
+  describe('effectMetadata', () => {
+    it('should get the effect metadata for a class instance with known effect name', () => {
+      class Fixture {
+        @Effect() a$: any;
+        @Effect({ dispatch: true })
+        b$: any;
+        @Effect({ dispatch: false })
+        c$: any;
+      }
+
+      const mock = new Fixture();
+
+      expect(effectMetadata(mock, 'a$')).toEqual({ dispatch: true });
+      expect(effectMetadata(mock, 'b$')).toEqual({ dispatch: true });
+      expect(effectMetadata(mock, 'c$')).toEqual({ dispatch: false });
+    });
+
+    it('should return "undefined" if the effect has not been decorated', () => {
+      class Fixture {
+        a$: any;
+      }
+
+      const mock = new Fixture();
+
+      expect(effectMetadata(mock, 'a$')).toBeUndefined();
+    });
+  });
 });

modules/effects/src/effects_metadata.ts

@@ -43,3 +43,16 @@ export const getSourceMetadata = compose(
   getEffectMetadataEntries,
   getSourceForInstance
 );
+
+export interface PartialEffectMetadata {
+  dispatch: boolean;
+}
+
+export function effectMetadata(
+  instance: any,
+  effectName: string
+): PartialEffectMetadata {
+  return getSourceMetadata(instance)
+    .filter(({ propertyName }) => propertyName === effectName)
+    .map(({ dispatch }) => ({ dispatch }))[0];
+}

modules/effects/src/index.ts

@@ -1,4 +1,4 @@
-export { Effect } from './effects_metadata';
+export { Effect, effectMetadata } from './effects_metadata';
 export { mergeEffects } from './effects_resolver';
 export { Actions } from './actions';
 export { EffectsModule } from './effects_module';