Run with colored output even within "pub run".

lib/src/io.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.io;
 
 import 'dart:async';
 import 'dart:io';
 
+// TODO(nweiz): Make this check [stdioType] once that works within "pub run".
 /// Whether "special" strings such as Unicode characters or color escapes are
 /// safe to use.
 ///
 /// On Windows or when not printing to a terminal, only printable ASCII
 /// characters should be used.
 bool get canUseSpecialChars =>
     Platform.operatingSystem != 'windows' &&
-    stdioType(stdout) == StdioType.TERMINAL;
+    Platform.environment["_UNITTEST_USE_COLOR"] != "false";
 
 /// Gets a "special" string (ANSI escape or Unicode).
 ///
 /// On Windows or when not printing to a terminal, returns something else since
 /// those aren't supported.
 String getSpecial(String special, [String onWindows = '']) =>
     canUseSpecialChars ? special : onWindows;
 
 /// Creates a temporary directory and passes its path to [fn].
 ///
 /// Once the [Future] returned by [fn] completes, the temporary directory and
 /// all its contents are deleted. [fn] can also return `null`, in which case
 /// the temporary directory is deleted immediately afterwards.
 ///
 /// Returns a future that completes to the value that the future returned from
 /// [fn] completes to.
 Future withTempDir(Future fn(String path)) {
   return new Future.sync(() {
     // TODO(nweiz): Empirically test whether sync or async functions perform
     // better here when starting a bunch of isolates.
     var tempDir = Directory.systemTemp.createTempSync('unittest_');
     return new Future.sync(() => fn(tempDir.path))
         .whenComplete(() => tempDir.deleteSync(recursive: true));
   });
 }