Add integration test coverage to the upgrader class

[danielbachhuber]

Given how critical a piece of software the upgrader class is, it would be ideal to have integration test coverage for it.

[danielbachhuber]

On this note, it would be helpful to have tests we could add to our own plugin to verify all of the integration aspects were working as expected.

[pippinsplugins]

I agree 100%. Hopefully we'll be writing a much better sample integration in the near future that could include full unit tests.