How can I write a unit test to determine whether an object can be garbage collected ?

Question

In relation to my previous question, I need to check whether a component that will be instantiated by Castle Windsor, can be garbage collected after my code has finished using it. I have tried the suggestion in the answers from the previous question, but it does not seem to work as expected, at least for my code. So I would like to write a unit test that tests whether a specific object instance can be garbage collected after some of my code has run.

Is that possible to do in a reliable way ?

EDIT

I currently have the following test based on Paul Stovell's answer, which succeeds:

     [TestMethod]
    public void ReleaseTest()
    {
        WindsorContainer container = new WindsorContainer();
        container.Kernel.ReleasePolicy = new NoTrackingReleasePolicy();
        container.AddComponentWithLifestyle<ReleaseTester>(LifestyleType.Transient);
        Assert.AreEqual(0, ReleaseTester.refCount);
        var weakRef = new WeakReference(container.Resolve<ReleaseTester>());
        Assert.AreEqual(1, ReleaseTester.refCount);
        GC.Collect();
        GC.WaitForPendingFinalizers();
        Assert.AreEqual(0, ReleaseTester.refCount, "Component not released");
    }

    private class ReleaseTester
    {
        public static int refCount = 0;

        public ReleaseTester()
        {
            refCount++;
        }

        ~ReleaseTester()
        {
            refCount--;
        }
    }

Am I right assuming that, based on the test above, I can conclude that Windsor will not leak memory when using the NoTrackingReleasePolicy ?

Answer 1

Perhaps you could hold a WeakReference to it and then check to see that it no longer alive (i.e., !IsAlive) after the tests have completed.

Answer 2

This is what I normally do:

[Test]
public void MyTest() 
{
    var reference = TestInternal();

    GC.Collect();
    GC.WaitForPendingFinalizers();
    Assert.IsNull(reference.Target);
}

private WeakReference TestInternal()
{
   var service = new Service();
   // Do things with service that might cause a memory leak...
   return new WeakReference(service, true);
   // Service should have gone out of scope about now, 
   // so the garbage collector can clean it up
}

NB: There are very, very few times where you should call GC.Collect() in a production application. But testing for leaks is one example of where it's appropriate.