Create unit tests for analyzer2dart/driver.

pkg/analyzer2dart/lib/src/driver.dart

 // Copyright (c) 2014, 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 analyzer2dart.driver;
 
 import 'package:analyzer/src/generated/element.dart';
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/java_io.dart';
 import 'package:analyzer/src/generated/sdk_io.dart';
@@ skipping 45 matching lines @@
 
   /**
    * Add the given file as the root of analysis, and return the corresponding
    * source.
    */
   Source setRealRoot(String path) {
     // Tell the analysis server about the root
     ChangeSet changeSet = new ChangeSet();
     JavaFile javaFile = new JavaFile(path);
     Source source = new FileBasedSource.con1(javaFile);
-    changeSet.addedSources.add(source);
+    changeSet.addedSource(source);
     context.applyChanges(changeSet);
     return source;
   }
+
+  /**
+   * Add the given file contents as the root of analysis.  For unit testing.
+   */
+  Source setFakeRoot(String contents) {
+    String path = 'root.dart';
+    // Tell the analysis server about the root
+    ChangeSet changeSet = new ChangeSet();
+    JavaFile javaFile = new JavaFile(path);
+    Source source = new FileBasedSource.con1(javaFile);
+    changeSet.addedSource(source);
+    changeSet.changedContent(source, contents);
+    context.applyChanges(changeSet);
+    return source;
+  }
 }