MONGOID-5661 [Monkey Patch Removal] Add test which checks for monkey patches

[johnnyshields]

Fixes MONGOID-5661

This PR adds a spec to check which kernel monkey patches Mongoid has added. It will help the team to remove them overtime, and will help ensure Mongoid developers do not add new monkey patches going forward.

[johnnyshields]

This spec dynamically monkey-patches Symbol, so I need to clean it up after the spec runs.

[jamis]

Hey Johnny, I like the idea behind this PR -- proactively looking for and reporting on new or removed monkey patches -- but it does not seem to play nice with the Mongoid.deprecate declarations. The source_location for deprecated methods are given a path to active_support/deprecation/method_wrappers.rb, where the wrapper methods are being declared, and thus are no longer reported as being under the mongoid source tree.

I'm not sure if there's a clean way to handle that case or not. Probably we can get by without this spec since the monkey patches in Mongoid seem to be encapsulated neatly in extension modules and are thus relatively easy to keep an eye on. Still, if you have any ideas for how to work around the deprecate issue, I'm interested.

[johnnyshields]

We can just ignore deprecated methods (i.e. not whitelist them in the spec).

The point of this spec is only to verify that "no new Monkey Patch methods are inadvertently added." The spec is not intended to assert that "certain Monkey Patch methods are present."

[johnnyshields]

@jamis I have added a @note comment explaining the above and have remove the deprecated methods from the list. This is ready for final review.

[jamis]

Thanks Johnny. I'm not sure why, but there's just something about this test--the test itself, not the implementation--that bothers me the more I think about it. I think I'm dubious about whether it will actually add value, or just get in the way...but I'm willing to give it the benefit of the doubt for now. I've merged it. We'll see what it does for us!