First stab at "pub run" command.

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

Index: sdk/lib/_internal/pub/test/run/utils.dart
diff --git a/sdk/lib/_internal/pub/test/run/utils.dart b/sdk/lib/_internal/pub/test/run/utils.dart
new file mode 100644
index 0000000000000000000000000000000000000000..6535b33bff9d650af556b9cceac23abc8b3be8c7
--- /dev/null
+++ b/sdk/lib/_internal/pub/test/run/utils.dart
@@ -0,0 +1,32 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS d.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 'package:scheduled_test/scheduled_process.dart';
+import 'package:scheduled_test/scheduled_test.dart';
+
+import '../test_pub.dart';
+
+/// Schedules starting the "pub run" process and validates the expected startup
+/// output.
+///
+/// if [transformers] is given, it should contain a list of transformer IDs
+/// (like "myapp/src/transformer") and this will validate that the output for
+/// loading those is shown.
+///
+/// Returns the `pub run` process.
+ScheduledProcess pubRun({Iterable<String> args,
+  Iterable<String> transformers}) {
+  var pub = startPub(args: ["run"]..addAll(args));
+
+  // This isn't normally printed, but the pub test infrastructure runs pub in
+  // verbose mode, which enables this.
+  pub.stdout.expect(startsWith("Loading source assets"));
+
+  if (transformers != null) {
+    for (var transformer in transformers) {
+      pub.stdout.expect(startsWith("Loading $transformer transformers"));
+    }
+  }
+  return pub;
+}