Make the tests work in the Dart repo.

lib/src/io.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.
 
 /// Helper functionality to make working with IO easier.
 library pub.io;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:convert';
@@ skipping 475 matching lines @@
 ///
 /// This works because when running from tests, pub always uses a snapshot named
 /// "pub.test.snapshot", which is not used outside of tests.
 final bool runningFromTest = Platform.script.path.endsWith('.test.snapshot');
 
 /// Whether pub is running from within the Dart SDK, as opposed to from the Dart
 /// source repository.
 final bool runningFromSdk =
     !runningFromTest && Platform.script.path.endsWith('.snapshot');
 
+/// A regular expression to match the script path of a pub script running from
+/// source in the Dart repo.
+final _dartRepoRegExp = new RegExp(
+    r"/third_party/pkg_tested/pub/(bin/pub.dart|test/.*_test\.dart)$");
+
 /// Whether pub is running from source in the Dart repo.
 ///
 /// This can happen when building Observatory, for example.
 final bool runningFromDartRepo =
-    Platform.script.path.endsWith('/third_party/pkg_tested/pub/bin/pub.dart');
+    Platform.script.path.contains(_dartRepoRegExp);
 
 /// Resolves [target] relative to the path to pub's `asset` directory.
 String assetPath(String target) => runningFromSdk
     ? sdkAssetPath(target)
     : path.join(pubRoot, 'lib', 'src', 'asset', target);
 
 /// Resolves [target] relative to the Dart SDK's `asset` directory.
 ///
 /// Throws a [StateError] if called from within the Dart repo.
 String sdkAssetPath(String target) {
@@ skipping 28 matching lines @@
 
 /// The path to the root of the Dart repo.
 ///
 /// This throws a [StateError] if it's called when not running pub from source
 /// in the Dart repo.
 final String dartRepoRoot = (() {
   if (!runningFromDartRepo) {
     throw new StateError("Not running from source in the Dart repo.");
   }
 
-  // In the Dart repo, the script is in "third_party/pkg_tested/pub/bin".
-  return path.dirname(path.dirname(path.dirname(path.dirname(path.dirname(
-      path.fromUri(Platform.script))))));
+  // Get the URL of the repo root in a way that works when either both running
+  // as a test or as a pub executable.
+  var url = Platform.script.replace(
+      path: Platform.script.path.replaceAll(_dartRepoRegExp, ''));
+  return path.fromUri(url);
 })();
 
 /// A line-by-line stream of standard input.
 final Stream<String> stdinLines = streamToLines(
     new ByteStream(stdin).toStringStream());
 
 /// Displays a message and reads a yes/no confirmation from the user.
 ///
 /// Returns a [Future] that completes to `true` if the user confirms or `false`
 /// if they do not.
@@ skipping 490 matching lines @@
 
   // TODO(rnystrom): Remove this and change to returning one string.
   static List<String> _toLines(String output) {
     var lines = splitLines(output);
     if (!lines.isEmpty && lines.last == "") lines.removeLast();
     return lines;
   }
 
   bool get success => exitCode == exit_codes.SUCCESS;
 }