First stab at a dev server in pub using barback.

sdk/lib/_internal/pub/test/serve/invalid_urls_test.dart

Index: sdk/lib/_internal/pub/test/serve/invalid_urls_test.dart
diff --git a/sdk/lib/_internal/pub/test/serve/invalid_urls_test.dart b/sdk/lib/_internal/pub/test/serve/invalid_urls_test.dart
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+// Copyright (c) 2013, 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.
+
+library pub_tests;
+
+import 'dart:io';
+
+import '../descriptor.dart' as d;
+import '../test_pub.dart';
+import 'utils.dart';
+
+main() {
+  initConfig();
+  integration("responds with a 404 on incomplete special URLs", () {
+    d.dir("foo", [
+      d.libPubspec("foo", "0.0.1")
+    ]).create();
+
+    d.dir(appPath, [
+      d.appPubspec({
+        "foo": {"path": "../foo"}
+      }),
+      // Make files that map to the special directory names to ensure they
+      // are *not* found.
+      d.dir("asset", [
+        d.file("packages"),
+        d.file("assets")
+      ]),
+      d.dir("lib", [
+        d.file("packages"),
+        d.file("assets")
+      ]),
+      d.dir("web", [
+        d.file("packages"),
+        d.file("assets")
+      ])
+    ]).create();
+
+    pubInstall();
+    startPubServe();
+    requestShould404("packages");
+    requestShould404("assets");
+    requestShould404("packages/");
+    requestShould404("assets/");
+    requestShould404("packages/myapp");
+    requestShould404("assets/myapp");
+    requestShould404("packages/myapp/");
+    requestShould404("assets/myapp/");
+    requestShould404("packages/foo");
+    requestShould404("assets/foo");
+    requestShould404("packages/foo/");
+    requestShould404("assets/foo/");
+    requestShould404("packages/unknown");
+    requestShould404("assets/unknown");
+    requestShould404("packages/unknown/");
+    requestShould404("assets/unknown/");
+    endPubServe();
+  });
+
+}