Issue #158 / #183 - add assertions for runtime config to unit test

Resolves issue brought up at #183 https://github.com/josegonzalez/cakephp-upload/pull/183 regarding not checking the result.

So I don't seem like a complete idiot, the test was 'working', and failing without my changes, because it asserts that handleUploadedFile will be called once only - and before, when the runtime config was not reset between saves, handleUploadedFile would get called twice. But yeah, I should have made it more explicit, like I've done here.

Signed-off-by: Joshua Paling <joshua.paling@gmail.com>