Add more tests and argument check to Process.sleep

sdk/lib/io/process.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.
 
 part of dart.io;
 
 // TODO(ager): The only reason for this class is that we
 // cannot patch a top-level at this point.
 class _ProcessUtils {
   external static _exit(int status);
@@ skipping 28 matching lines @@
   _ProcessUtils._setExitCode(status);
 }
 
 /**
  * Sleep for the duration specified in [duration].
  *
  * Use this with care, as no asynchronous operations can be processed
  * in a isolate while it is blocked in a [sleep] call.
  */
 void sleep(Duration duration) {
-  _ProcessUtils._sleep(duration.inMilliseconds);
+  int milliseconds = duration.inMilliseconds;
+  if (milliseconds < 0) {
+    throw new ArgumentError("sleep: duration cannot be negative");
+  }
+  _ProcessUtils._sleep(milliseconds);
 }
 
 /**
  * [Process] is used to start new processes using the static
  * [start] and [run] methods.
  */
 abstract class Process {
   /**
    * Starts a process running the [executable] with the specified
    * [arguments]. Returns a [:Future<Process>:] that completes with a
@@ skipping 210 matching lines @@
   /**
    * Contains the system message for the process exception if any.
    */
   final String message;
 
   /**
    * Contains the OS error code for the process exception if any.
    */
   final int errorCode;
 }