Add a flag to control the use of color in the test runner.

bin/unittest.dart

 // Copyright (c) 2015, 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 unittest.unittest;
 
 import 'dart:async';
 import 'dart:io';
 import 'dart:isolate';
 
 import 'package:args/args.dart';
 import 'package:stack_trace/stack_trace.dart';
 
 import 'package:unittest/src/runner/console_reporter.dart';
 import 'package:unittest/src/runner/load_exception.dart';
 import 'package:unittest/src/runner/loader.dart';
 import 'package:unittest/src/util/exit_codes.dart' as exit_codes;
 import 'package:unittest/src/util/io.dart';
 import 'package:unittest/src/utils.dart';
 
 /// The argument parser used to parse the executable arguments.
 final _parser = new ArgParser();
 
 void main(List<String> args) {
   _parser.addFlag("help", abbr: "h", negatable: false,
       help: "Shows this usage information.");
   _parser.addOption("package-root", hide: true);
+  _parser.addFlag("color", defaultsTo: null,
+      help: 'Whether to use terminal colors.\n(auto-detected by default)');
 
   var options;
   try {
     options = _parser.parse(args);
   } on FormatException catch (error) {
     _printUsage(error.message);
     exitCode = exit_codes.usage;
     return;
   }
 
@@ skipping 13 matching lines @@
       }
       paths = ["test"];
     }
 
     return Future.wait(paths.map((path) {
       if (new Directory(path).existsSync()) return loader.loadDir(path);
       if (new File(path).existsSync()) return loader.loadFile(path);
       throw new LoadException(path, 'Does not exist.');
     }));
   }).then((suites) {
-    var reporter = new ConsoleReporter(flatten(suites));
+    var color = options["color"];
+    if (color == null) color = canUseSpecialChars;
+    var reporter = new ConsoleReporter(flatten(suites), color: color);
     return reporter.run().then((success) {
       exitCode = success ? 0 : 1;
     }).whenComplete(() => reporter.close());
   }).catchError((error, stackTrace) {
     if (error is LoadException) {
       // TODO(nweiz): color this message?
       stderr.writeln(getErrorMessage(error));
 
       // Only print stack traces for load errors that come from the user's 
       if (error.innerError is! IOException &&
@@ skipping 36 matching lines @@
     output = stderr;
   }
 
   output.write("""$message
 
 Usage: pub run unittest:unittest [files or directories...]
 
 ${_parser.usage}
 """);
 }