Add basic support for a configuration file.

lib/src/util/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.
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 import 'dart:mirrors';
 
 import 'package:path/path.dart' as p;
@@ skipping 24 matching lines @@
   var os = OperatingSystem.findByIoName(name);
   if (os != null) return os;
 
   throw new UnsupportedError('Unsupported operating system "$name".');
 })();
 
 /// A queue of lines of standard input.
 final stdinLines = new StreamQueue(
     UTF8.decoder.fuse(const LineSplitter()).bind(stdin));
 
+/// Whether this is being run as a subprocess in the test package's own tests.
+bool inTestTests = Platform.environment["_DART_TEST_TESTING"] == "true";
+
 /// The root directory below which to nest temporary directories created by the
 /// test runner.
 ///
 /// This is configurable so that the test code can validate that the runner
 /// cleans up after itself fully.
 final _tempDir = Platform.environment.containsKey("_UNITTEST_TEMP_DIR")
     ? Platform.environment["_UNITTEST_TEMP_DIR"]
     : Directory.systemTemp.path;
 
 /// The path to the `lib` directory of the `test` package.
 String libDir({String packageRoot}) {
   var pathToIo = libraryPath(#test.util.io, packageRoot: packageRoot);
   return p.dirname(p.dirname(p.dirname(pathToIo)));
 }
 
 // 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' &&
-    Platform.environment["_UNITTEST_USE_COLOR"] != "false";
+    Platform.operatingSystem != 'windows' && !inTestTests;
 
 /// Creates a temporary directory and returns its path.
 String createTempDir() =>
     new Directory(_tempDir).createTempSync('dart_test_').path;
 
 /// 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.
@@ skipping 94 matching lines @@
 ///
 /// This has a built-in race condition: another process may bind this port at
 /// any time after this call has returned. If at all possible, callers should
 /// use [getUnusedPort] instead.
 Future<int> getUnsafeUnusedPort() async {
   var socket = await RawServerSocket.bind(InternetAddress.LOOPBACK_IP_V4, 0);
   var port = socket.port;
   await socket.close();
   return port;
 }