How do I unit test a finalizer?
- by GraemeF
I have the following class which is a decorator for an IDisposable object (I have omitted the stuff it adds) which itself implements IDisposable using a common pattern:
public class DisposableDecorator : IDisposable
{
private readonly IDisposable _innerDisposable;
public DisposableDecorator(IDisposable innerDisposable)
{
_innerDisposable = innerDisposable;
}
#region IDisposable Members
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
#endregion
~DisposableDecorator()
{
Dispose(false);
}
protected virtual void Dispose(bool disposing)
{
if (disposing)
_innerDisposable.Dispose();
}
}
I can easily test that innerDisposable is disposed when Dispose() is called:
[Test]
public void Dispose__DisposesInnerDisposable()
{
var mockInnerDisposable = new Mock<IDisposable>();
new DisposableDecorator(mockInnerDisposable.Object).Dispose();
mockInnerDisposable.Verify(x => x.Dispose());
}
But how do I write a test to make sure innerDisposable does not get disposed by the finalizer? I want to write something like this but it fails, presumably because the finalizer hasn't been called by the GC thread:
[Test]
public void Finalizer__DoesNotDisposeInnerDisposable()
{
var mockInnerDisposable = new Mock<IDisposable>();
new DisposableDecorator(mockInnerDisposable.Object);
GC.Collect();
mockInnerDisposable.Verify(x => x.Dispose(), Times.Never());
}
