Improve pub's pubspec error messages.

sdk/lib/_internal/pub/test/get/git/dependency_name_match_pubspec_test.dart

Index: sdk/lib/_internal/pub/test/get/git/dependency_name_match_pubspec_test.dart
diff --git a/sdk/lib/_internal/pub/test/get/git/dependency_name_match_pubspec_test.dart b/sdk/lib/_internal/pub/test/get/git/dependency_name_match_pubspec_test.dart
index 0a1f6451bc085aaf00b18afa68ee5d9fe43c3460..880a25136815fd12131092231d97965fff56ca2d 100644
--- a/sdk/lib/_internal/pub/test/get/git/dependency_name_match_pubspec_test.dart
+++ b/sdk/lib/_internal/pub/test/get/git/dependency_name_match_pubspec_test.dart
@@ -4,6 +4,9 @@
 
 library pub_tests;
 
+import 'package:scheduled_test/scheduled_test.dart';
+
+import '../../../lib/src/exit_codes.dart' as exit_codes;
 import '../../descriptor.dart' as d;
 import '../../test_pub.dart';
 
@@ -24,7 +27,7 @@ main() {
       })
     ]).create();
 
-    pubGet(error: new RegExp(r'"name" field "foo" doesn' "'" r't match '
-        r'expected name "weirdname"\.'));
+    pubGet(error: contains('"name" field doesn\'t match expected name '
+        '"weirdname".'), exitCode: exit_codes.DATA);
   });
 }