Specs for check_unmodified_since and destroy_conditionally

Remove byebug statement

Specs for destroy_conditionally, unmodified_since

Use mocks to test these methods correctly

Fix static analysis errors

WIP invalid check unmodified

Remove invalid check_unmodified_since

Add more detailed specs

Better specs for check_unmodified_since

Add negative case for destroy_conditionally!

Improve negative destroy_conditionally spec

Fix destroy_conditionally specs

Simplify negative destroy_conditionally tests

Remove redundant expects

Fix type in unmodified_since header

Fix time header

Simulate Grape throwing symbol

Remove unused allow symbols

Simply destroy_conditionally! specs

Change test description