Make Java test more reliable (#18863)

src/SignalR/clients/java/signalr/src/test/java/com/microsoft/signalr/HubConnectionTest.java

@@ -2256,14 +2256,12 @@ class HubConnectionTest {
 
         hubConnection.start().timeout(1, TimeUnit.SECONDS).blockingAwait();
 
-        TimeUnit.MILLISECONDS.sleep(100);
-        hubConnection.stop().timeout(1, TimeUnit.SECONDS).blockingAwait();
+        String message = mockTransport.getNextSentMessage().timeout(1, TimeUnit.SECONDS).blockingGet();
+        assertEquals("{\"type\":6}" + RECORD_SEPARATOR, message);
+        message = mockTransport.getNextSentMessage().timeout(1, TimeUnit.SECONDS).blockingGet();
+        assertEquals("{\"type\":6}" + RECORD_SEPARATOR, message);
 
-        String[] sentMessages = mockTransport.getSentMessages();
-        assertTrue(sentMessages.length > 1);
-        for (int i = 1; i < sentMessages.length; i++) {
-            assertEquals("{\"type\":6}" + RECORD_SEPARATOR, sentMessages[i]);
-        }
+        hubConnection.stop().timeout(1, TimeUnit.SECONDS).blockingAwait();
     }
 
     @Test

src/SignalR/clients/java/signalr/src/test/java/com/microsoft/signalr/MockTransport.java

@@ -7,6 +7,7 @@ import java.util.ArrayList;
 
 import io.reactivex.Completable;
 import io.reactivex.subjects.CompletableSubject;
+import io.reactivex.subjects.SingleSubject;
 
 class MockTransport implements Transport {
     private OnReceiveCallBack onReceiveCallBack;
@@ -17,6 +18,7 @@ class MockTransport implements Transport {
     final private boolean autoHandshake;
     final private CompletableSubject startSubject = CompletableSubject.create();
     final private CompletableSubject stopSubject = CompletableSubject.create();
+    private SingleSubject<String> sendSubject = SingleSubject.create();
 
     private static final String RECORD_SEPARATOR = "\u001e";
 
@@ -51,6 +53,8 @@ class MockTransport implements Transport {
     public Completable send(String message) {
         if (!(ignorePings && message.equals("{\"type\":6}" + RECORD_SEPARATOR))) {
             sentMessages.add(message);
+            sendSubject.onSuccess(message);
+            sendSubject = SingleSubject.create();
         }
         return Completable.complete();
     }
@@ -89,6 +93,10 @@ class MockTransport implements Transport {
         return sentMessages.toArray(new String[sentMessages.size()]);
     }
 
+    public SingleSubject<String> getNextSentMessage() {
+        return sendSubject;
+    }
+
     public String getUrl() {
         return this.url;
     }