Make ActionController::Caching::Sweeper class thread safe

[Angelmmiguel]

The current implementation of ActionController::Caching::Sweeper is not Thread safe and it may cause issues in multi-thread environments. The problem is that @controller variable is lost in the different Threads. For sweepers with big loops, it might cause the following error:

undefined method `expire_action' for #<ReleaseSweeper:0x000000073b69b8 @_routes=nil, @controller=nil>

Changes

• Store the controller variable in a current Thread property
• Fix a deprecation message with minitest

This closes #71

[Angelmmiguel]

@rafaelfranca I'm a bit afraid of the compatibility of this PR with the current usage of the gem. I see some people suggesting to use @controller ||= ActionController::Base.new to avoid @controller to be nil. However, with these changes, the code will be different:

self.controller ||= ActionController::Base.new

[Angelmmiguel]

@rafaelfranca Should I perform any other change? :)

[rafaelfranca]

I think it is fine. If people want to avoid nil they can use the writer.

[rafaelfranca]

I think you can remove this comment

[Angelmmiguel]

Done @rafaelfranca !