Test.dart will wait for the temporary directory to be deleted before exiting.

tools/testing/dart/test_runner.dart

 // Copyright (c) 2011, 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("test_runner");
 
 #import("status_file_parser.dart");
 #import("test_progress.dart");
 #import("test_suite.dart");
 
@@ skipping 461 matching lines @@
         } else if (!_temporaryDirectory.startsWith('/tmp/') ||
                    _temporaryDirectory.contains('/../')) {
           // Let's be extra careful, since rm -rf is so dangerous.
           print('Temporary directory $_temporaryDirectory unsafe to delete!');
           _progress.allDone();
         } else {
           // TODO(dart:1211): Use delete(recursive=true) in Dart when it is
           // implemented, and add Windows support.
           var deletion =
               new Process.start('/bin/rm', ['-rf', _temporaryDirectory]);
-          deletion.startHandler = (){
+          deletion.exitHandler = (int exitCode) {
+            if (exitCode == 0) {
+              print('\nTemporary directory $_temporaryDirectory deleted.');
+            } else {
+              print('\nDeletion of temp dir $_temporaryDirectory failed.');
+            }
             _progress.allDone();
           };
         }
       }
     }
   }
 
   void _runTest(TestCase test) {
     _progress.testAdded();
     _tests.add(test);
@@ skipping 42 matching lines @@
           test.displayName != 'dartc/junit_tests') {
         _ensureDartcBatchRunnersStarted(test.executablePath);
         _getDartcBatchRunnerProcess().startTest(test);
       } else {
         new RunningProcess(test).start();
       }
       _numProcesses++;
     }
   }
 }