[Fix #169] Add new Minitest/SkipEnsure cop

[koic]

Closes #169.

This cop checks that ensure call even if skip. It is unexpected that ensure will be called when skipping test.
If conditional skip is used, it checks that ensure is also called conditionally.

On the other hand, it accepts skip used in rescue because ensure may be teardown process to begin setup process.

# bad
def test_skip
  skip 'This test is skipped.'

  assert 'foo'.present?
ensure
  do_something
end

# bad
def test_conditional_skip
  skip 'This test is skipped.' if condition

  assert do_something
ensure
  do_teardown
end

# good
def test_skip
  skip 'This test is skipped.'

  begin
    assert 'foo'.present?
  ensure
    do_something
  end
end

# good
def test_conditional_skip
  skip 'This test is skipped.' if condition

  assert do_something
ensure
  if condition
    do_teardown
  end
end

# good
def test_skip_is_used_in_rescue
  do_setup
  assert do_something
rescue
  skip 'This test is skipped.'
ensure
  do_teardown
end

---

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• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
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• Commit message starts with [Fix #issue-number] (if the related issue exists).
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[koic]

@yahonda I'm worried about the cop name. It may be abstract, but the cop name Minitest/SkipEnsure cop is simple name.
I would like to hear because you are the author of the issue.
Which of Minitest/EnsureCallEvenIfSkip cop or Minitest/SkipEnsure cop is easier to understand as a user? Of course there may be even better names. If you have any ideas, please share it.

[yahonda]

Let me have time to think about the cop's name.

[yahonda]

I like Minitest/SkipEnsure than Minitest/EnsureCallEvenIfSkip because it is short.
and how about Minitest/EnsureNotSkipped ?

[koic]

Thank you for your feedback and suggestion. I'll take the simplest Minitest/SkipEnsure, including the suggested name.

[koic]

@yahonda RuboCop Minitest 0.20 has been released.

[yahonda]

Thanks for implementing Minitest/SkipEnsure cop and releasing RuboCop Minitest 0.20. Let me take a look at this and open a pull request to rails/rails.

[yahonda]

Opened rails/rails#45216