To ensure tests don't step on each others toes, make sure we back up
the static properties of the global App class before running tests that
modify any of these properties.
Just a basic test to ensure that the module `get()` method behaves
somewhat reasonable when no query params are given.
Had to make a small change to the Rpost module itself. Since the
`$_SESSION` superglobal may not always be set (and is not in the test),
use `isset` instead of `array_key_exists` to check if we have saved
query params in the session.
In general, isset is safer than array_key_exists if there's a chance
that the array itself may not exist.
