Add following tests :

runtime/observatory/tests/service/developer_server_control_test.dart

Index: runtime/observatory/tests/service/developer_server_control_test.dart
diff --git a/runtime/observatory/tests/service/developer_server_control_test.dart b/runtime/observatory/tests/service/developer_server_control_test.dart
index fc1e9405cf4fcd4e0e4cbfa7ff6a0bf5687dbb30..400796b8eeb8b3a3907886c80c8752b1482e7b8a 100644
--- a/runtime/observatory/tests/service/developer_server_control_test.dart
+++ b/runtime/observatory/tests/service/developer_server_control_test.dart
@@ -9,12 +9,63 @@ 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 = [