Fix flaky health check test

src/csharp/Grpc.HealthCheck.Tests/HealthServiceImplTest.cs

@@ -201,18 +201,22 @@ namespace Grpc.HealthCheck.Tests
         {
             var cts = new CancellationTokenSource();
             var context = new TestServerCallContext(cts.Token);
-            var writer = new TestResponseStreamWriter();
+            var writer = new TestResponseStreamWriter(started: false);
 
             var impl = new HealthServiceImpl();
             var callTask = impl.Watch(new HealthCheckRequest { Service = "" }, writer, context);
 
-            // Write new 10 statuses. Only last 5 statuses will be returned when we read them from watch writer
+            // Write new statuses. Only last statuses will be returned when we read them from watch writer
             for (var i = 0; i < HealthServiceImpl.MaxStatusBufferSize * 2; i++)
             {
                 // These statuses aren't "valid" but it is useful for testing to have an incrementing number
-                impl.SetStatus("", (HealthCheckResponse.Types.ServingStatus)i);
+                impl.SetStatus("", (HealthCheckResponse.Types.ServingStatus)i + 10);
             }
 
+            // Start reading responses now that statuses have been queued up
+            // This is to keep the test non-flakey
+            writer.Start();
+
             // Read messages in a background task
             var statuses = new List<HealthCheckResponse.Types.ServingStatus>();
             var readStatusesTask = Task.Run(async () => {
@@ -240,11 +244,11 @@ namespace Grpc.HealthCheck.Tests
             Assert.AreEqual(HealthCheckResponse.Types.ServingStatus.ServiceUnknown, statuses[0]);
 
             // Last 5 queued messages
-            Assert.AreEqual((HealthCheckResponse.Types.ServingStatus)5, statuses[1]);
+            Assert.AreEqual((HealthCheckResponse.Types.ServingStatus)15, statuses[statuses.Count - 5]);
-            Assert.AreEqual((HealthCheckResponse.Types.ServingStatus)6, statuses[2]);
+            Assert.AreEqual((HealthCheckResponse.Types.ServingStatus)16, statuses[statuses.Count - 4]);
-            Assert.AreEqual((HealthCheckResponse.Types.ServingStatus)7, statuses[3]);
+            Assert.AreEqual((HealthCheckResponse.Types.ServingStatus)17, statuses[statuses.Count - 3]);
-            Assert.AreEqual((HealthCheckResponse.Types.ServingStatus)8, statuses[4]);
+            Assert.AreEqual((HealthCheckResponse.Types.ServingStatus)18, statuses[statuses.Count - 2]);
-            Assert.AreEqual((HealthCheckResponse.Types.ServingStatus)9, statuses[5]);
+            Assert.AreEqual((HealthCheckResponse.Types.ServingStatus)19, statuses[statuses.Count - 1]);
         }
 #endif
 

src/csharp/Grpc.HealthCheck.Tests/TestResponseStreamWriter.cs

@@ -25,24 +25,42 @@ namespace Grpc.HealthCheck.Tests
 {
     internal class TestResponseStreamWriter : IServerStreamWriter<HealthCheckResponse>
     {
-        private Channel<HealthCheckResponse> _channel;
+        private readonly Channel<HealthCheckResponse> _channel;
+        private readonly TaskCompletionSource<object> _startTcs;
 
-        public TestResponseStreamWriter(int maxCapacity = 1)
+        public TestResponseStreamWriter(int maxCapacity = 1, bool started = true)
         {
             _channel = System.Threading.Channels.Channel.CreateBounded<HealthCheckResponse>(new BoundedChannelOptions(maxCapacity) {
                 SingleReader = false,
                 SingleWriter = true,
                 FullMode = BoundedChannelFullMode.Wait
             });
+            if (!started)
+            {
+                _startTcs = new TaskCompletionSource<object>(TaskCreationOptions.RunContinuationsAsynchronously);
+            }
         }
 
         public ChannelReader<HealthCheckResponse> WrittenMessagesReader => _channel.Reader;
 
         public WriteOptions WriteOptions { get; set; }
 
-        public Task WriteAsync(HealthCheckResponse message)
+        public async Task WriteAsync(HealthCheckResponse message)
         {
-            return _channel.Writer.WriteAsync(message).AsTask();
+            if (_startTcs != null)
+            {
+                await _startTcs.Task;
+            }
+
+            await _channel.Writer.WriteAsync(message);
+        }
+
+        public void Start()
+        {
+            if (_startTcs != null)
+            {
+                _startTcs.TrySetResult(null);
+            }
         }
 
         public void Complete()

src/csharp/Grpc.HealthCheck/HealthServiceImpl.cs

@@ -157,9 +157,6 @@ namespace Grpc.HealthCheck
         {
             string service = request.Service;
 
-            HealthCheckResponse response = GetHealthCheckResponse(service, throwOnNotFound: false);
-            await responseStream.WriteAsync(response);
-
             // Channel is used to to marshall multiple callers updating status into a single queue.
             // This is required because IServerStreamWriter is not thread safe.
             //
@@ -205,6 +202,10 @@ namespace Grpc.HealthCheck
                 channel.Writer.Complete();
             });
 
+            // Send current status immediately
+            HealthCheckResponse response = GetHealthCheckResponse(service, throwOnNotFound: false);
+            await responseStream.WriteAsync(response);
+
             // Read messages. WaitToReadAsync will wait until new messages are available.
             // Loop will exit when the call is canceled and the writer is marked as complete.
             while (await channel.Reader.WaitToReadAsync())