Async-step, first cut.

runtime/observatory/tests/service/command_test.dart

Index: runtime/observatory/tests/service/command_test.dart
diff --git a/runtime/observatory/tests/service/command_test.dart b/runtime/observatory/tests/service/command_test.dart
index 9403662976b6e7f00dc989bb17f0aa71d4a6e8c7..69ac08f3968a890b3ae71d2194fe028fd5a45633 100644
--- a/runtime/observatory/tests/service/command_test.dart
+++ b/runtime/observatory/tests/service/command_test.dart
@@ -185,7 +185,7 @@ void testCommandRunNotFound() {
   RootCommand cmd = new RootCommand([new TestCommand(out, 'alpha', [])]);
 
   cmd.runCommand('goose').catchError(expectAsync((e) {
-      expect(e, equals('notfound'));
+      expect(e, equals('No such command'));
   }));
 }
 
@@ -196,7 +196,7 @@ void testCommandRunAmbiguous() {
                                      new TestCommand(out, 'ankle', [])]);
 
   cmd.runCommand('a 55').catchError(expectAsync((e) {
-      expect(e, equals('ambiguous'));
+      expect(e, equals('Ambiguous command'));
       out.clear();
       cmd.runCommand('ankl 55').then(expectAsync((_) {
           expect(out.toString(), equals('executing ankle([55])\n'));