Attempt to get more data from multiple_isolate_list_test

tests/standalone/vmservice/test_helper.dart

Index: tests/standalone/vmservice/test_helper.dart
diff --git a/tests/standalone/vmservice/test_helper.dart b/tests/standalone/vmservice/test_helper.dart
index 9de301ef02785a4f99f97f688eb3b11c0ef68eef..fed4631ceabf1e8c49c41254bbf3ea97f7662c26 100644
--- a/tests/standalone/vmservice/test_helper.dart
+++ b/tests/standalone/vmservice/test_helper.dart
@@ -48,11 +48,19 @@ abstract class VmServiceRequestHelper {
       onRequestFailed(e);
       return;
     }
-    // Received a map.
-    Expect.isTrue(reply is Map);
-    // Has a 'type' key.
-    Expect.isNotNull(reply['type']);
-    onRequestCompleted(reply);
+    if (reply is! Map) {
+        onRequestFailed('Reply was not a map: $reply');
+        return;
+    }
+    if (reply['type'] == null) {
+        onRequestFailed('Reply does not contain a type key: $reply');
+        return;
+    }
+    try {
+        onRequestCompleted(reply);
+    } catch(e) {
+        onRequestFailed('Test callback failed: $e');
+    }
   }
 
   void onRequestFailed(dynamic error) {