Improve default support provided for plugins

pkg/analyzer_plugin/test/utilities/subscriptions/subscription_manager_test.dart

 // Copyright (c) 2017, 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 'package:analyzer_plugin/protocol/protocol_generated.dart';
 import 'package:analyzer_plugin/utilities/subscriptions/subscription_manager.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
 void main() {
   defineReflectiveTests(SubscriptionManagerTest);
 }
 
 @reflectiveTest
 class SubscriptionManagerTest {
   SubscriptionManager manager = new SubscriptionManager();
 
   test_servicesForFile() {
     expect(manager.servicesForFile('/project/lib/test.dart'), hasLength(0));
   }
 
   test_setSubscriptions() {
-    manager.setSubscriptions({
-      AnalysisService.HIGHLIGHTS: [
-        '/project/lib/foo.dart',
-        '/project/lib/bar.dart'
-      ],
-      AnalysisService.NAVIGATION: ['/project/lib/foo.dart']
+    String fooPath = '/project/lib/foo.dart';
+    String barPath = '/project/lib/bar.dart';
+    String bazPath = '/project/lib/baz.dart';
+    //
+    // Set the initial set of subscriptions.
+    //
+    Map<String, List<AnalysisService>> newSubscriptions =
+        manager.setSubscriptions({
+      AnalysisService.HIGHLIGHTS: [fooPath, barPath],
+      AnalysisService.NAVIGATION: [fooPath]
     });
-    expect(manager.servicesForFile('/project/lib/test.dart'), hasLength(0));
-    expect(manager.servicesForFile('/project/lib/bar.dart'),
-        unorderedEquals([AnalysisService.HIGHLIGHTS]));
+
     expect(
-        manager.servicesForFile('/project/lib/foo.dart'),
+        manager.servicesForFile(fooPath),
         unorderedEquals(
             [AnalysisService.HIGHLIGHTS, AnalysisService.NAVIGATION]));
+    expect(manager.servicesForFile(barPath),
+        unorderedEquals([AnalysisService.HIGHLIGHTS]));
+    expect(manager.servicesForFile(bazPath), hasLength(0));
+
+    expect(
+        newSubscriptions[fooPath],
+        unorderedEquals(
+            [AnalysisService.HIGHLIGHTS, AnalysisService.NAVIGATION]));
+    expect(newSubscriptions[barPath],
+        unorderedEquals([AnalysisService.HIGHLIGHTS]));
+    //
+    // Update the subscriptions.
+    //
+    newSubscriptions = manager.setSubscriptions({
+      AnalysisService.HIGHLIGHTS: [bazPath, barPath],
+      AnalysisService.NAVIGATION: [barPath]
+    });
+
+    expect(manager.servicesForFile(fooPath), hasLength(0));
+    expect(
+        manager.servicesForFile(barPath),
+        unorderedEquals(
+            [AnalysisService.HIGHLIGHTS, AnalysisService.NAVIGATION]));
+    expect(manager.servicesForFile(bazPath),
+        unorderedEquals([AnalysisService.HIGHLIGHTS]));
+
+    expect(newSubscriptions[barPath],
+        unorderedEquals([AnalysisService.NAVIGATION]));
+    expect(newSubscriptions[bazPath],
+        unorderedEquals([AnalysisService.HIGHLIGHTS]));
   }
 }