Prevent intermittent NPE in queue tests (#19301)

There appears to be an intermittent NPE in queue tests relating to the deferred
shutdown/terminate functions.

This PR more formally asserts that shutdown and termination occurs before starting
and finishing the tests but leaves the defer in place to ensure that if there is an
issue shutdown/termination will occur.

Signed-off-by: Andrew Thornton <art27@cantab.net>

modules/queue/queue_channel_test.go

@@ -128,6 +128,8 @@ func TestChannelQueue_Pause(t *testing.T) {
 	queueShutdown := []func(){}
 	queueTerminate := []func(){}
 
+	terminated := make(chan struct{})
+
 	queue, err = NewChannelQueue(handle,
 		ChannelQueueConfiguration{
 			WorkerPoolConfiguration: WorkerPoolConfiguration{
@@ -142,15 +144,18 @@ func TestChannelQueue_Pause(t *testing.T) {
 		}, &testData{})
 	assert.NoError(t, err)
 
-	go queue.Run(func(shutdown func()) {
-		lock.Lock()
-		defer lock.Unlock()
-		queueShutdown = append(queueShutdown, shutdown)
-	}, func(terminate func()) {
-		lock.Lock()
-		defer lock.Unlock()
-		queueTerminate = append(queueTerminate, terminate)
-	})
+	go func() {
+		queue.Run(func(shutdown func()) {
+			lock.Lock()
+			defer lock.Unlock()
+			queueShutdown = append(queueShutdown, shutdown)
+		}, func(terminate func()) {
+			lock.Lock()
+			defer lock.Unlock()
+			queueTerminate = append(queueTerminate, terminate)
+		})
+		close(terminated)
+	}()
 
 	// Shutdown and Terminate in defer
 	defer func() {
@@ -278,4 +283,30 @@ func TestChannelQueue_Pause(t *testing.T) {
 	}
 	assert.Equal(t, test1.TestString, result1.TestString)
 	assert.Equal(t, test1.TestInt, result1.TestInt)
+
+	lock.Lock()
+	callbacks := make([]func(), len(queueShutdown))
+	copy(callbacks, queueShutdown)
+	queueShutdown = queueShutdown[:0]
+	lock.Unlock()
+	// Now shutdown the queue
+	for _, callback := range callbacks {
+		callback()
+	}
+
+	// terminate the queue
+	lock.Lock()
+	callbacks = make([]func(), len(queueTerminate))
+	copy(callbacks, queueTerminate)
+	queueShutdown = queueTerminate[:0]
+	lock.Unlock()
+	for _, callback := range callbacks {
+		callback()
+	}
+	select {
+	case <-terminated:
+	case <-time.After(10 * time.Second):
+		assert.Fail(t, "Queue should have terminated")
+		return
+	}
 }