Revert "fix: IdleWatermark unit test (#640)"

This reverts commit 0c79113.

pkg/forward/forward_test.go

@@ -247,17 +247,31 @@ func TestNewInterStepDataForwardIdleWatermark(t *testing.T) {
 	assert.True(t, to1.IsEmpty())
 
 	stopped := f.Start()
-	assert.True(t, fromStep.IsEmpty())
 	// first batch: read message size is 1 with one ctrl message
 	// the ctrl message should be acked
 	// no message published to the next vertex
 	// so the timeline should be empty
+	var wg sync.WaitGroup
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		for fromStep.IsEmpty() {
+			select {
+			case <-ctx.Done():
+				if ctx.Err() == context.DeadlineExceeded {
+					err = ctx.Err()
+				}
+			default:
+				time.Sleep(1 * time.Millisecond)
+			}
+		}
+	}()
 	_, errs := fromStep.Write(ctx, ctrlMessage)
 	assert.Equal(t, make([]error, 1), errs)
+	wg.Wait()
 	if err != nil {
 		t.Fatal("expected the buffer not to be empty", err)
 	}
-	// waiting for the ctrl message to be acked
 	for !fromStep.IsEmpty() {
 		select {
 		case <-ctx.Done():
@@ -268,16 +282,11 @@ func TestNewInterStepDataForwardIdleWatermark(t *testing.T) {
 			time.Sleep(1 * time.Millisecond)
 		}
 	}
-	// it should not publish any wm because
-	// 1. readLength != 0
-	// 2. we only have one ctrl message
-	// 3. meaning dataMessage=0
 	otNil, _ := otStores["to1"].GetAllKeys(ctx)
 	assert.Nil(t, otNil)
 
 	// 2nd and 3rd batches: read message size is 0
 	// should send idle watermark
-	var wg sync.WaitGroup
 	wg.Add(1)
 	go func() {
 		defer wg.Done()