Avoid to mask all the NetworkRpcException

runtime/observatory/tests/service/test_helper.dart

Index: runtime/observatory/tests/service/test_helper.dart
diff --git a/runtime/observatory/tests/service/test_helper.dart b/runtime/observatory/tests/service/test_helper.dart
index 1d2ea9d54dec24b1ab974940b3970138cb865a76..0e8b6e932af424b757e26dcf039252d1c5dd47f0 100644
--- a/runtime/observatory/tests/service/test_helper.dart
+++ b/runtime/observatory/tests/service/test_helper.dart
@@ -310,7 +310,14 @@ class _ServiceTesterRunner {
         await process.requestExit();
       }, onError: (e, st) {
         process.requestExit();
-        if (!_isWebSocketDisconnect(e)) {
+        // TODO: remove this workaround.
+        // This is necessary due to non awaited operations.
+        // E.G. object.dart (398~402)
+        // When an exception is thrown inside a test (directly or via await) the
+        // stacktrace is non-null and shows where the exception has been thrown.
+        // If vice versa the exception is due to an error in a non-awaited
+        // Future the stacktrace is null.
+        if (st != null || !_isWebSocketDisconnect(e)) {
           print('Unexpected exception in service tests: $e $st');
           throw e;
         }