In Castle Windsor 3, override an existing component registration in a unit test

There are two things that you have to do to create an overriding instance:

1. Assign it a unique name
2. Call the IsDefault method

So to get the example to work:

this.WindsorContainer.Register(
   Component.For<IMediaPlayerProxyFactory>()
      .Instance(mockMediaPlayerProxyFactory)
      .IsDefault()
      .Named("OverridingFactory")
);

Because I plan to use this overriding patten in many tests, I’ve created my own extension method:

public static class TestWindsorExtensions
{
    public static ComponentRegistration<T> OverridesExistingRegistration<T>(
       this ComponentRegistration<T> componentRegistration
    ) where T : class
    {
        return componentRegistration
           .Named(Guid.NewGuid().ToString())
           .IsDefault();
    }
}

Now the example can be simplified to:

this.WindsorContainer.Register(
   Component.For<IMediaPlayerProxyFactory>()
      .Instance(mockMediaPlayerProxyFactory)
      .OverridesExistingRegistration()
);

Later Edit

Version 3.1 introduces the IsFallback method. If I register all my initial components with IsFallback, then any new registrations will automatically override these initial registrations. I would have gone down that path if the functionality was available at the time.

https://github.com/castleproject/Windsor/blob/master/docs/whats-new-3.1.md#fallback-components