[AIT-358] fix: tests with append scenarios

Realtime behavior has changed:

- first message after append is a full message with `MESSAGE_UPDATE` type
- second and next messages will be only with delta and `MESSAGE_APPEND` type

Author: ttypic

lib/src/test/java/io/ably/lib/test/common/Helpers.java

@@ -956,6 +956,12 @@ public synchronized void waitFor() {
             } catch(InterruptedException e) {}
         }
 
+        public synchronized void reset() {
+            gotResult = false;
+            result = null;
+            error = null;
+        }
+
         public T result;
         public ErrorInfo error;
         private boolean gotResult = false;

lib/src/test/java/io/ably/lib/test/realtime/RealtimeChannelMessageEditTest.java

@@ -385,13 +385,23 @@ public void appendMessage_checkUpdatedData() throws Exception {
         messageAppend.data = "Append data";
         channel.appendMessage(messageAppend);
 
+        appendWaiter.waitFor();
+
         // 3. Verify update
         Message retrieved = waitForUpdatedMessageAppear(channel, serial);
         assertEquals("Expected updated data in history", "Initial dataAppend data", retrieved.data);
         assertEquals("Expected MESSAGE_UPDATE action in history", MessageAction.MESSAGE_UPDATE, retrieved.action);
-        assertEquals("Expected MESSAGE_APPEND action through realtime", MessageAction.MESSAGE_APPEND, appendWaiter.result.action);
-        assertEquals("Expected delta through realtime", "Append data", appendWaiter.result.data);
+        assertEquals("Expected MESSAGE_UPDATE only for the first time from realtime", MessageAction.MESSAGE_UPDATE, appendWaiter.result.action);
+        assertEquals("Expected full message data through realtime", "Initial dataAppend data", appendWaiter.result.data);
 
+        appendWaiter.reset();
+
+        channel.appendMessage(messageAppend);
+
+        appendWaiter.waitFor();
+
+        assertEquals("Expected MESSAGE_APPEND action through realtime", MessageAction.MESSAGE_APPEND, appendWaiter.result.action);
+        assertEquals("Expected only delta through realtime", "Append data", appendWaiter.result.data);
     }
 
     private PaginatedResult<Message> waitForMessageAppearInVersionHistory(Channel channel, String serial, Param[] params, Predicate<Message[]> predicate) throws Exception {