Improve pub's pubspec error messages.

sdk/lib/_internal/pub/test/pub_get_and_upgrade_test.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 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';
 
 main() {
   initConfig();
 
   forBothPubGetAndUpgrade((command) {
     group('requires', () {
       integration('a pubspec', () {
         d.dir(appPath, []).create();
 
         pubCommand(command,
             error: new RegExp(r'Could not find a file named "pubspec.yaml" '
                 r'in "[^\n]*"\.'));
       });
 
       integration('a pubspec with a "name" key', () {
         d.dir(appPath, [
           d.pubspec({"dependencies": {"foo": null}})
         ]).create();
 
-        pubCommand(command, error: new RegExp(r'Missing the required "name" '
-            r'field\.'));
+        pubCommand(command,
+            error: contains('Missing the required "name" field.'),
+            exitCode: exit_codes.DATA);
       });
     });
 
     integration('adds itself to the packages', () {
       // The symlink should use the name in the pubspec, not the name of the
       // directory.
       d.dir(appPath, [
         d.pubspec({"name": "myapp_name"}),
         d.libDir('myapp_name')
       ]).create();
@@ skipping 71 matching lines @@
           error: new RegExp("^Incompatible dependencies on baz:\n"));
     });
 
     integration('does not allow a dependency on itself', () {
       d.dir(appPath, [
         d.appPubspec({
           "myapp": {"path": "."}
         })
       ]).create();
 
-      pubCommand(command, error: new RegExp(r'"dependencies.myapp": Package '
-          r'may not list itself as a dependency\.'));
+      pubCommand(command,
+          error: contains('A package may not list itself as a dependency.'),
+          exitCode: exit_codes.DATA);
     });
 
     integration('does not allow a dev dependency on itself', () {
       d.dir(appPath, [
         d.pubspec({
           "name": "myapp",
           "dev_dependencies": {
             "myapp": {"path": "."}
           }
         })
       ]).create();
 
-      pubCommand(command, error: new RegExp(r'"dev_dependencies.myapp": '
-          r'Package may not list itself as a dependency\.'));
+      pubCommand(command,
+          error: contains('A package may not list itself as a dependency.'),
+          exitCode: exit_codes.DATA);
     });
   });
 }