Add a test for tags to configuration_test.

test/runner/configuration/configuration_test.dart

 // Copyright (c) 2016, 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.
 
 @TestOn("vm")
 
 import 'package:boolean_selector/boolean_selector.dart';
 import 'package:path/path.dart' as p;
 import 'package:test/test.dart';
 
@@ skipping 165 matching lines @@
         var older = new Configuration(
             testOn: new PlatformSelector.parse("vm"));
         var newer = new Configuration(
             testOn: new PlatformSelector.parse("linux"));
         var merged = older.merge(newer);
         expect(merged.testOn,
             equals(new PlatformSelector.parse("vm && linux")));
       });
     });
 
-    group("for tags", () {
+    group("for include and excludeTags", () {
       test("if neither is defined, preserves the default", () {
         var merged = new Configuration().merge(new Configuration());
         expect(merged.includeTags, equals(BooleanSelector.all));
         expect(merged.excludeTags, equals(BooleanSelector.none));
       });
 
       test("if only the old configuration's is defined, uses it", () {
         var merged = new Configuration(
                 includeTags: new BooleanSelector.parse("foo || bar"),
                 excludeTags: new BooleanSelector.parse("baz || bang"))
@@ skipping 25 matching lines @@
             excludeTags: new BooleanSelector.parse("qux"));
         var merged = older.merge(newer);
 
         expect(merged.includeTags,
             equals(new BooleanSelector.parse("(foo || bar) && blip")));
         expect(merged.excludeTags,
             equals(new BooleanSelector.parse("(baz || bang) || qux")));
       });
     });
 
+    group("for tags", () {
+      test("merges each nested configuration", () {
+        var merged = new Configuration(
+          tags: {
+            new BooleanSelector.parse("foo"):
+                new Configuration(verboseTrace: true),
+            new BooleanSelector.parse("bar"): new Configuration(jsTrace: true)
+          }
+        ).merge(new Configuration(
+          tags: {
+            new BooleanSelector.parse("bar"): new Configuration(jsTrace: false),
+            new BooleanSelector.parse("baz"): new Configuration(skip: true)
+          }
+        ));
+
+        expect(merged.tags[new BooleanSelector.parse("foo")].verboseTrace,
+            isTrue);
+        expect(merged.tags[new BooleanSelector.parse("bar")].jsTrace, isFalse);
+        expect(merged.tags[new BooleanSelector.parse("baz")].skip, isTrue);
+      });
+    });
+
     group("for timeout", () {
       test("if neither is defined, preserves the default", () {
         var merged = new Configuration().merge(new Configuration());
         expect(merged.timeout, equals(new Timeout.factor(1)));
       });
 
       test("if only the old configuration's is defined, uses it", () {
         var merged = new Configuration(timeout: new Timeout.factor(2))
             .merge(new Configuration());
         expect(merged.timeout, equals(new Timeout.factor(2)));
@@ skipping 39 matching lines @@
         expect(merged.onPlatform[new PlatformSelector.parse("vm")].verboseTrace,
             isTrue);
         expect(merged.onPlatform[new PlatformSelector.parse("chrome")].jsTrace,
             isFalse);
         expect(merged.onPlatform[new PlatformSelector.parse("firefox")].skip,
             isTrue);
       });
     });
   });
 }