Support passing configuration data to a transformer plugin.

sdk/lib/_internal/pub/test/pubspec_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 pubspec_test;
 
 import 'package:unittest/unittest.dart';
 
 import '../lib/src/pubspec.dart';
 import '../lib/src/source.dart';
@@ skipping 196 matching lines @@
 
       expectFormatError('author: 123');
       expectFormatError('author: {not: {a: string}}');
       expectFormatError('author: [not, ok]');
     });
 
     test("throws if both 'author' and 'authors' are present", () {
       expectFormatError('{author: abe, authors: ted}');
     });
 
+    test("throws if a transformer isn't a string or map", () {
+      expectFormatError('{transformers: 12}');
+      expectFormatError('{transformers: [12]}');
+    });
+
+    test("throws if a transformer's configuration isn't a map", () {
+      expectFormatError('{transformers: {pkg: 12}}');
+    });
+
     test("allows comment-only files", () {
       var pubspec = new Pubspec.parse(null, '''
 # No external dependencies yet
 # Including for completeness
 # ...and hoping the spec expands to include details about author, version, etc
 # See http://www.dartlang.org/docs/pub-package-manager/ for details
 ''', sources);
       expect(pubspec.version, equals(Version.none));
       expect(pubspec.dependencies, isEmpty);
     });
@@ skipping 42 matching lines @@
 
       test("throws if the sdk isn't a valid version constraint", () {
         expectFormatError('''
 environment:
   sdk: "oopies"
 ''');
       });
     });
   });
 }