Add a test runner executable.

lib/src/exit_codes.dart

Index: lib/src/exit_codes.dart
diff --git a/lib/src/exit_codes.dart b/lib/src/exit_codes.dart
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+// 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.
+
+/// Exit code constants.
+///
+/// From [the BSD sysexits manpage][manpage]. Not every constant here is used.
+///
+/// [manpage]: http://www.freebsd.org/cgi/man.cgi?query=sysexits
+library unittest.exit_codes;
+
+/// The command completely successfully.
+const success = 0;
+
+/// The command was used incorrectly.
+const usage = 64;
+
+/// The input data was incorrect.
+const data = 65;
+
+/// An input file did not exist or was unreadable.
+const noInput = 66;
+
+/// The user specified did not exist.
+const noUser = 67;
+
+/// The host specified did not exist.
+const noHost = 68;
+
+/// A service is unavailable.
+const unavailable = 69;
+
+/// An internal software error has been detected.
+const software = 70;
+
+/// An operating system error has been detected.
+const os = 71;
+
+/// Some system file did not exist or was unreadable.
+const osFile = 72;
+
+/// A user-specified output file cannot be created.
+const cantCreate = 73;
+
+/// An error occurred while doing I/O on some file.
+const io = 74;
+
+/// Temporary failure, indicating something that is not really an error.
+const tempFail = 75;
+
+/// The remote system returned something invalid during a protocol exchange.
+const protocol = 76;
+
+/// The user did not have sufficient permissions.
+const noPerm = 77;
+
+/// Something was unconfigured or mis-configured.
+const config = 78;