Re-enable color-sniffing in unittest's VM configuration.

pkg/unittest/lib/vm_config.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.
 
 /**
  * A simple unit test library for running tests on the VM.
  */
 library unittest_vm_config;
 
 import 'dart:async';
 import 'dart:io';
 import 'unittest.dart';
 
 class VMConfiguration extends SimpleConfiguration {
   // Color constants used for generating messages.
   final String GREEN_COLOR = '\u001b[32m';
   final String RED_COLOR = '\u001b[31m';
   final String MAGENTA_COLOR = '\u001b[35m';
   final String NO_COLOR = '\u001b[0m';
 
   // We make this public so the user can turn it off if they want.
   bool useColor;
 
   VMConfiguration()
       : super(),
-        // TODO(nweiz): Re-enable this when issue 13712 is fixed.
-        // useColor = stdioType(stdout) == StdioType.TERMINAL;
-        useColor = false;
+        useColor = stdioType(stdout) == StdioType.TERMINAL;
 
   String formatResult(TestCase testCase) {
     String result = super.formatResult(testCase);
     if (useColor) {
       if (testCase.result == PASS) {
         return "${GREEN_COLOR}${result}${NO_COLOR}";
       } else if (testCase.result == FAIL) {
         return "${RED_COLOR}${result}${NO_COLOR}";
       } else if (testCase.result == ERROR) {
         return "${MAGENTA_COLOR}${result}${NO_COLOR}";
@@ skipping 21 matching lines @@
       exit(status);
     });
   }
 }
 
 void useVMConfiguration() {
   unittestConfiguration = _singleton;
 }
 
 final _singleton = new VMConfiguration();