Should succeed (?)
Tests decoupled - notice the tearDown() override in AccessPreferencesTest

Also, in AccessPreferencesTest, ctx and prefs are no more static (no reason
they were in the first place).

I also squashed null keys tests together and corrected the points that
I had misunderstood due to coupling

For a simpler Raw sets test see :
http://stackoverflow.com/questions/19610569/
android-sharedpreferences-null-keys-values-and-sets-corner-cases
Same link for the weird prefs behaviors.
Dump reflection in tearDown() +comments for bogus CCEs due to test coupling
AccessPreferences -> null keys are disallowed - test NPE is thrown + readme