title: Testing a ngrx effect that in one case does not dispatch a new action
body: <p>I have this one effect where some preconditions have to be true so that a specific action gets dispatched:</p>
  
  <pre><code>@Effect()
  prepareLoadDetails$: Observable&lt;Action&gt; = this.actions$
      .ofType(PREPARE_LOAD_DETAILS)
      .withLatestFrom(this.store)
      .filter(([actionType, stateStore]) =&gt; this.necessarySelectionsMade(stateStore))
      .map(() =&gt; {
          return new LoadDetailsAction();
      });
  </code></pre>
  
  <p>Now I'm somehow stuck in unit testing this code. There's no problem getting the LoadDetailsAction dispatched. But how can I test that no action is dispatched in the other cases?</p>
  
  <pre><code>describe('prepareLoadDetails$', () =&gt; {
      it('should trigger a LoadDetailsAction if all needed selections are made', (done) =&gt; {
          // given
          const {runner, effects} = setup({
              // some setup of state here
          });
  
          // when
          runner.queue(new PrepareLoadDetailsAction());
  
          // then
          effects.prepareLoadDetails$.subscribe(result =&gt; {
              expect(result).toEqual(new LoadDetailsAction());
              done();
          });
      });
  
      it('should not trigger a LoadDetailsAction if needed selections are not made', (done) =&gt; {
          // given
          const {runner, effects} = setup({
              // some other setup of state here
          });
  
          // when
          runner.queue(new PrepareLoadDetailsAction());
  
          // then ???
      });
  });
  </code></pre>