tests: Assert connection error code rather than message

The error messages are subject to change, but the codes are not, so
assert the code instead.

Signed-off-by: Lewis Marshall <[email protected]>

Author: lmars

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

@@ -1669,7 +1669,7 @@ public void channel_invalid_resume_reattach_channels() throws AblyException {
 
             ErrorInfo resumeError = connectionWaiter.waitFor(ConnectionState.connected);
             assertNotNull(resumeError);
-            assertTrue(resumeError.message.contains("Invalid connection key"));
+            assertEquals("Verify error code indicates invalid connection key", resumeError.code, 80018);
             assertSame(resumeError, ably.connection.connectionManager.getStateErrorInfo());
             assertNotEquals("A new connection was created", originalConnectionId, ably.connection.id);