Friday, May 14, 2010

NInject, NHibernate, and unit testing

I recently came across an interesting problem in my tests. In the application I am working on, I have recently created a framework for generating tag numbers for pieces of equipment. I put unit tests around the code and decided that the system was complex enough to warrant some integration tests.

The set up for the integration tests is quite complex as I have to not only set up an NHibernate session, but also the Ninject kernel. In my app the way I bind the NHibernate session is through the following line:

Bind<ISession>().ToMethod(c => NHibernateSessionFactory.Instance.OpenSession()).InRequestScope();

In my integration test SetUp I create a session for the test to use and start a transaction. In the TearDown I rollback the transaction and dispose the session. So I needed to manually change the binding to ISession in Ninject. I did that using the following code

foreach (var binding in _kernel.GetBindings(typeof (ISession)))
_kernel.Bind<ISession>().ToMethod(c => _session).InRequestScope();

(I would love if anyone suggested a better way to do this)

The integration test was working fine. Until I started working on another completely unrelated module for doing auditing on certain changes to domain objects. Once the module was finished I ran the entire build again and the integration tests started failing with a message that the ISession object was closed. If they were run independently or even as part of an entire integration tests run, they passed. I finally figured out that they would only fail, when they were being run together with the tests for this new module.

The culprit turned out to be this line of code I was running in the TestFixtureSetUp for the auditing tests:

HttpContext.Current = new HttpContext(new HttpRequest(string.Empty, "", string.Empty), new HttpResponse(new StringWriter()));

Since the HttpContext.Current was staying the same, the integration tests were only ever providing one ISession instance for all of the tagging integration tests. So once the first test ran and disposed of the session, any other components that required an ISession were still getting the old disposed instance of the ISession. The fix was simple, I just had to set HttpContext.Current back to null in the TestFixtureTearDown for the audit module test.