First stab at "pub run" command.

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

Index: sdk/lib/_internal/pub/test/run/runs_app_in_entrypoint_test.dart
diff --git a/sdk/lib/_internal/pub/test/run/runs_app_in_entrypoint_test.dart b/sdk/lib/_internal/pub/test/run/runs_app_in_entrypoint_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..f9a020922ec9e0d789b905cc999c4c935bd8f0bb
--- /dev/null
+++ b/sdk/lib/_internal/pub/test/run/runs_app_in_entrypoint_test.dart
@@ -0,0 +1,34 @@
+// Copyright (c) 2014, 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 '../descriptor.dart' as d;
+import '../test_pub.dart';
+import 'utils.dart';
+
+const SCRIPT = """
+import 'dart:io';
+
+main() {
+  stdout.writeln("stdout output");
+  stderr.writeln("stderr output");
+  exitCode = 123;
+}
+""";
+
+main() {
+  initConfig();
+  integration('runs a Dart application in the entrypoint package', () {
+    d.dir(appPath, [
+      d.appPubspec(),
+      d.dir("bin", [
+        d.file("script.dart", SCRIPT)
+      ])
+    ]).create();
+
+    var pub = pubRun(args: ["script"]);
+    pub.stdout.expect("stdout output");
+    pub.stderr.expect("stderr output");
+    pub.shouldExit(123);
+  });
+}