Add tests for BuildGroup names

tools/gardening/lib/src/util.dart

Index: tools/gardening/lib/src/util.dart
diff --git a/tools/gardening/lib/src/util.dart b/tools/gardening/lib/src/util.dart
index e7ea13461a4c1695b4d8f59614bd617855d31da8..f21703aba560c0d9c327e1afa43612dcc5ac5d86 100644
--- a/tools/gardening/lib/src/util.dart
+++ b/tools/gardening/lib/src/util.dart
@@ -43,11 +43,24 @@ void log(Object text) {
   if (LOG) print(text);
 }
 
+class HttpException implements Exception {
+  final Uri uri;
+  final int statusCode;
+
+  HttpException(this.uri, this.statusCode);
+
+  String toString() => '$uri: $statusCode';
+}
+
 /// Reads the content of [uri] as text.
 Future<String> readUriAsText(HttpClient client, Uri uri) async {
   HttpClientRequest request = await client.getUrl(uri);
   HttpClientResponse response = await request.close();
-  return await response.transform(UTF8.decoder).join();
+  if (response.statusCode != 200) {
+    response.drain();
+    throw new HttpException(uri, response.statusCode);
+  }
+  return response.transform(UTF8.decoder).join();
 }
 
 ArgParser createArgParser() {