Clean up various ways we find paths in pub.

sdk/lib/_internal/pub/test/test_pub.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.
 
 /// Test infrastructure for testing pub. Unlike typical unit tests, most pub
 /// tests are integration tests that stage some stuff on the file system, run
 /// pub, and then validate the results. This library provides an API to build
 /// tests like that.
 library test_pub;
 
@@ skipping 254 matching lines @@
     currentSchedule.onComplete.schedule(() => deleteEntry(_sandboxDir),
         'deleting the sandbox directory');
 
     // Schedule the test.
     body();
   });
 }
 
 /// Get the path to the root "pub/test" directory containing the pub
 /// tests.
-String get testDirectory {
-  var dir = new Options().script;
-  while (path.basename(dir) != 'test') dir = path.dirname(dir);
-
-  return path.absolute(dir);
-}
+String get testDirectory =>
+  path.absolute(path.dirname(libraryPath('test_pub')));
 
 /// Schedules renaming (moving) the directory at [from] to [to], both of which
 /// are assumed to be relative to [sandboxDir].
 void scheduleRename(String from, String to) {
   schedule(
       () => renameDir(
           path.join(sandboxDir, from),
           path.join(sandboxDir, to)),
       'renaming $from to $to');
 }
@@ skipping 339 matching lines @@
   bool matches(item, MatchState matchState) {
     if (item is! Pair) return false;
     return _firstMatcher.matches(item.first, matchState) &&
         _lastMatcher.matches(item.last, matchState);
   }
 
   Description describe(Description description) {
     description.addAll("(", ", ", ")", [_firstMatcher, _lastMatcher]);
   }
 }