fix: schedule output of ReactiveCommand.Execute (#1325)

Fixes #1318

Author: kentcb

src/ReactiveUI.Tests/ReactiveCommandTest.cs

@@ -311,26 +311,18 @@ public void ExecutePassesThroughParameter()
         }
 
         [Fact]
-        public void ExecuteExecutesOnTheSpecifiedScheduler()
+        public void ExecuteResultIsDeliveredOnSpecifiedScheduler()
         {
             (new TestScheduler()).With(sched => {
-                var execute = Observables.Unit.Delay(TimeSpan.FromSeconds(1), sched);
+                var execute = Observables.Unit;
                 var fixture = ReactiveCommand.CreateFromObservable(() => execute, outputScheduler: sched);
-                var isExecuting = fixture
-                    .IsExecuting
-                    .CreateCollection();
+                var executed = false;
 
-                fixture.Execute().Subscribe();
-                sched.AdvanceByMs(999);
+                fixture.Execute().Subscribe(_ => executed = true);
 
-                Assert.Equal(2, isExecuting.Count);
-                Assert.False(isExecuting[0]);
-                Assert.True(isExecuting[1]);
-
-                sched.AdvanceByMs(2);
-
-                Assert.Equal(3, isExecuting.Count);
-                Assert.False(isExecuting[2]);
+                Assert.False(executed);
+                sched.AdvanceByMs(1);
+                Assert.True(executed);
             });
         }
 

src/ReactiveUI/ReactiveCommand.cs

@@ -842,7 +842,8 @@ public override IDisposable Subscribe(IObserver<TResult> observer)
                             return Observable.Throw<TResult>(ex);
                         })
                     .PublishLast()
-                    .RefCount();
+                    .RefCount()
+                    .ObserveOn(this.outputScheduler);
             } catch (Exception ex) {
                 this.exceptions.OnNext(ex);
                 return Observable.Throw<TResult>(ex);