Put in a teardown for the docs test, fixed dom.py to actually run it correctly, added PRESUMBIT.

tools/dom/docs/test/docs_test.dart

 // Copyright (c) 2013, 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 docs_test;
 
 import 'dart:io';
 
 import 'package:unittest/unittest.dart';
 
 import '../bin/docs.dart';
 import '../lib/docs.dart';
 
 final testJsonPath = scriptDir.append('test.json').canonicalize();
 
 main() {
-  test('Ensure that docs.json is up to date', () {
+  group('docs', () {
     var oldJson = new File.fromPath(json_path);
     var testJson = new File.fromPath(testJsonPath);
 
-    // We should find a json file where we expect it.
-    expect(oldJson.existsSync(), isTrue);
-
-    // Save the last modified time to check it at the end.
-    var oldJsonModified = oldJson.lastModifiedSync();
-
-    // There should be no test file yet.
-    if (testJson.existsSync()) testJson.deleteSync();
-    expect(testJson.existsSync(), isFalse);
-
-    expect(convert(lib_path, testJsonPath)
-        .then((bool anyErrors) {
-      expect(anyErrors, isFalse);
-
-      // We should have a file now.
-      expect(testJson.existsSync(), isTrue);
-
-      // Ensure that there's nothing different between the new JSON and old.
-      expect(testJson.readAsStringSync(), equals(oldJson.readAsStringSync()));
-
-      // Ensure that the old JSON file didn't actually change.
-      expect(oldJsonModified, equals(oldJson.lastModifiedSync()));
-
+    tearDown(() {
       // Clean up.
       if (testJson.existsSync()) {
         testJson.deleteSync();
       }
-      expect(testJson.existsSync(), isFalse);
-    }), completes);
+      assert(!testJson.existsSync());
+    });
+
+    test('Ensure that docs.json is up to date', () {
+      // We should find a json file where we expect it.
+      expect(oldJson.existsSync(), isTrue);
+
+      // Save the last modified time to check it at the end.
+      var oldJsonModified = oldJson.lastModifiedSync();
+
+      // There should be no test file yet.
+      if (testJson.existsSync()) testJson.deleteSync();
+      assert(!testJson.existsSync());
+
+      expect(convert(lib_path, testJsonPath)
+          .then((bool anyErrors) {
+        expect(anyErrors, isFalse);
+
+        // We should have a file now.
+        expect(testJson.existsSync(), isTrue);
+
+        // Ensure that there's nothing different between the new JSON and old.
+        expect(testJson.readAsStringSync(), equals(oldJson.readAsStringSync()));
+
+        // Ensure that the old JSON file didn't actually change.
+        expect(oldJsonModified, equals(oldJson.lastModifiedSync()));
+      }), completes);
+    });
   });
 }