Use backtracking when solving dependency constraints.

utils/tests/pub/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;
 
 import 'dart:async';
 import 'dart:collection' show Queue;
 import 'dart:io';
 import 'dart:json' as json;
 import 'dart:math';
 import 'dart:uri';
 import 'dart:utf';
 
 import 'package:http/testing.dart';
 import 'package:oauth2/oauth2.dart' as oauth2;
 import 'package:pathos/path.dart' as path;
 import 'package:scheduled_test/scheduled_process.dart';
 import 'package:scheduled_test/scheduled_server.dart';
 import 'package:scheduled_test/scheduled_test.dart';
+import 'package:unittest/unittest.dart' as unittest;
 import 'package:yaml/yaml.dart';
 
 import '../../pub/entrypoint.dart';
 // TODO(rnystrom): Using "gitlib" as the prefix here is ugly, but "git" collides
 // with the git descriptor method. Maybe we should try to clean up the top level
 // scope a bit?
 import '../../pub/git.dart' as gitlib;
 import '../../pub/git_source.dart';
 import '../../pub/hosted_source.dart';
 import '../../pub/http.dart';
 import '../../pub/io.dart';
 import '../../pub/path_source.dart';
 import '../../pub/safe_http_server.dart';
 import '../../pub/system_cache.dart';
 import '../../pub/utils.dart';
 import '../../pub/validator.dart';
 import 'command_line_config.dart';
 import 'descriptor.dart' as d;
 
 /// This should be called at the top of a test file to set up an appropriate
 /// test configuration for the machine running the tests.
 initConfig() {
   // If we aren't running on the bots, use the human-friendly config.
   if (new Options().arguments.contains('--human')) {
-    configure(new CommandLineConfiguration());
+    unittest.unittestConfiguration = new CommandLineConfiguration();
   }
 }
 
 /// The current [HttpServer] created using [serve].
 var _server;
 
 /// The cached value for [_portCompleter].
 Completer<int> _portCompleterCache;
 
 /// The completer for [port].
@@ skipping 540 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]);
   }
 }