In the previous parts of this short series (that took a long time to finish) I looked at testing code that depends on pinvoke calls. I did this by wrapping the PInvoked functions in a class and then injecting that class into the depending code. I used the wrapper class to put some checks around the platform invokes to smooth some rough edges of the calls to unmanaged land. This creates a nice reusable interface around these calls but now we have the same problem we started with, testability. In this post I'll look at adding a final layer of indirection to be able to test this code.