Added new duplicated_test_run cop

[ignacio-chiazzo]

Added new duplicated_test_run cop

If a Minitest class inherits from another class, it will also inherit its methods causing Minitest to run the parent's tests methods twice.

This PR detects when there are two tests classes, one inherits from the other, and both have tests methods. MinitestRubocop will add an offence to the Child class in such a case.

For example:

class B < Minitest::Test
  test "test 1" do 
      #....
  end

  class A < B
    test "test 2" do 
        #....
    end 
  end
end

It will run test_1 twice!

I came across a few PRs/pieces of code using subclassing. I wrote a Gem that detects duplicated test run during Runtime and a Post with more details.

This cop has some limitations:

• It only works if both classes are on the same file.
• Using describes also has the same problem, and the cop doesn't detect it (yet ;)).

More information in this post.

[koic]

Nice! Can you squash your commits into one?

[koic]

Thanks!