Add following tests :

runtime/observatory/tests/service/developer_server_control_test.dart

 // Copyright (c) 2014, 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.
 // VMOptions=--error_on_bad_type --error_on_bad_override
 
 import 'dart:async';
 import 'dart:developer';
 import 'package:observatory/service_io.dart';
 import 'package:unittest/unittest.dart';
 import 'test_helper.dart';
 
+int majorVersion;
+int minorVersion;
+Uri serverUri;
+
 Future<Null> testeeBefore() async {
   print('testee before');
-  print(await Service.getInfo());
-  // Start the web server.
-  ServiceProtocolInfo info = await Service.controlWebServer(enable: true);
-  print(info);
+  // First grab the URL where the observatory is listening on and the
+  // service protocol version numbers. We expect the URL to be null as
+  // the server has not been started yet.
+  ServiceProtocolInfo info = await Service.getInfo();
+  majorVersion = info.majorVersion;
+  minorVersion = info.minorVersion;
+  serverUri = info.serverUri;
+  expect(info.serverUri, isNull);
+  {
+    // Now, start the web server and store the URI which is expected to be
+    // non NULL in the top level variable.
+    ServiceProtocolInfo info = await Service.controlWebServer(enable: true);
+    expect(info.majorVersion, equals(majorVersion));
+    expect(info.minorVersion, equals(minorVersion));
+    expect(info.serverUri, isNotNull);
+    serverUri = info.serverUri;
+  }
+  {
+    // Now try starting the web server again, this should just return the
+    // existing state without any change (port number does not change).
+    ServiceProtocolInfo info = await Service.controlWebServer(enable: true);
+    expect(info.majorVersion, equals(majorVersion));
+    expect(info.minorVersion, equals(minorVersion));
+    expect(info.serverUri, equals(serverUri));
+  }
+  {
+    // Try turning off the web server, this should turn off the server and
+    // the Uri returned should be null.
+    ServiceProtocolInfo info = await Service.controlWebServer(enable: false);
+    expect(info.majorVersion, equals(majorVersion));
+    expect(info.minorVersion, equals(minorVersion));
+    expect(info.serverUri, isNull);
+  }
+  {
+    // Try turning off the web server again, this should be a nop
+    // and the Uri returned should be null.
+    ServiceProtocolInfo info = await Service.controlWebServer(enable: false);
+    expect(info.majorVersion, equals(majorVersion));
+    expect(info.minorVersion, equals(minorVersion));
+    expect(info.serverUri, isNull);
+  }
+  {
+    // Start the web server again for the test below.
+    ServiceProtocolInfo info = await Service.controlWebServer(enable: true);
+    majorVersion = info.majorVersion;
+    minorVersion = info.minorVersion;
+    serverUri = info.serverUri;
+    expect(info.majorVersion, equals(majorVersion));
+    expect(info.minorVersion, equals(minorVersion));
+    expect(info.serverUri, equals(serverUri));
+  }
 }
 
 var tests = [
 (Isolate isolate) async {
   await isolate.reload();
   // Just getting here means that the testee enabled the service protocol
   // web server.
   expect(true, true);
 }
 ];
 
 main(args) => runIsolateTests(args,
                               tests,
                               testeeBefore: testeeBefore,
                               // the testee is responsible for starting the
                               // web server.
                               testeeControlsServer: true);