Demonstrate how reg can be used for testing applications

[thedrow]

The DI nature of reg allows us to replace the entire system with fakes, mocks, stubs without using unittest.mock.
This means that testing is much easier because you don't have to know the call site.
Maybe we can add a TestCase base class that cleans up the registry after each test.

[faassen]

A belated thanks for this suggestion!

An application does need to use Reg in order to be able to replace the behavior of a function. Perhaps you could write a sample app and/or documentation to demonstrate this? A test case base class might also be useful, but this also depends on the testing framework in use; a py.test setup and teardown for instance might also be useful.

[thedrow]

I've got a lot on my plate at the moment. Keep this open and I'll get to it.