Add basic support for a configuration file.

test/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.
 
 // TODO(nweiz): Remove this tag when we can get [packageDir] working without it
 // (dart-lang/sdk#24022).
 library test.test.io;
 
 import 'dart:async';
 import 'dart:io';
@@ skipping 84 matching lines @@
 StreamMatcher containsInOrder(Iterable<String> strings) =>
     inOrder(strings.map((string) => consumeThrough(contains(string))));
 
 /// Runs the test executable with the package root set properly.
 ///
 /// If [forwardStdio] is true, the standard output and error from the process
 /// will be printed as part of the parent test. This is used for debugging.
 ScheduledProcess runTest(List args, {String reporter,
     int concurrency, Map<String, String> environment,
     bool forwardStdio: false}) {
-  reporter ??= "expanded";
   concurrency ??= 1;
 
   var allArgs = [
     p.absolute(p.join(packageDir, 'bin/test.dart')),
     "--package-root=${p.join(packageDir, 'packages')}",
-    "--concurrency=$concurrency",
-    "--reporter=$reporter"
-  ]..addAll(args);
+    "--concurrency=$concurrency"
+  ];
+  if (reporter != null) allArgs.add("--reporter=$reporter");
+  allArgs.addAll(args);
 
   if (environment == null) environment = {};
-  environment.putIfAbsent("_UNITTEST_USE_COLOR", () => "false");
+  environment.putIfAbsent("_DART_TEST_TESTING", () => "true");
 
   var process = runDart(allArgs,
       environment: environment,
       description: "dart bin/test.dart");
 
   if (forwardStdio) {
     process.stdoutStream().listen(print);
     process.stderrStream().listen(print);
   }
 
@@ skipping 45 matching lines @@
     var match;
     while (match == null) {
       var line = await pub.stdout.next();
       match = _servingRegExp.firstMatch(line);
     }
     _pubServePortCompleter.complete(int.parse(match[1]));
   }, "waiting for pub serve to emit its port number");
 
   return pub;
 }