First stab at "pub run" command.

sdk/lib/_internal/pub/test/run/nonexistent_script_test.dart

Index: sdk/lib/_internal/pub/test/run/nonexistent_script_test.dart
diff --git a/sdk/lib/_internal/pub/test/barback/fails_if_args_with_all_test.dart b/sdk/lib/_internal/pub/test/run/nonexistent_script_test.dart
similarity index 56%
copy from sdk/lib/_internal/pub/test/barback/fails_if_args_with_all_test.dart
copy to sdk/lib/_internal/pub/test/run/nonexistent_script_test.dart
index 42f79431d630a6b1ac02ab1945d9c6988860acef..cb233b38b4530ea6eea8260ebc8f1ecf1cfcf9c7 100644
--- a/sdk/lib/_internal/pub/test/barback/fails_if_args_with_all_test.dart
+++ b/sdk/lib/_internal/pub/test/run/nonexistent_script_test.dart
@@ -2,8 +2,6 @@
 // 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 'package:scheduled_test/scheduled_test.dart';
-
 import '../../lib/src/exit_codes.dart' as exit_codes;
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
@@ -11,13 +9,13 @@ import 'utils.dart';
 
 main() {
   initConfig();
+  integration('Errors if the script does not exist.', () {
+    d.dir(appPath, [
+      d.appPubspec()
+    ]).create();
 
-  setUp(() {
-    d.appDir().create();
+    var pub = pubRun(args: ["script"]);
+    pub.stderr.expect("Could not find bin/script.dart.");
+    pub.shouldExit(exit_codes.NO_INPUT);
   });
-
-  pubBuildAndServeShouldFail("if a directory is passed with --all",
-      args: ["example", "--all"],
-      error: 'Directory names are not allowed if "--all" is passed.',
-      exitCode: exit_codes.USAGE);
 }