[Fix #255] Add new Minitest/AssertOperator and Minitest/RefuteOperator cops

[koic]

Fixes #255.

This PR adds new Minitest/AssertOperator and Minitest/RefuteOperator cops.

Minitest/AssertOperator cop

This cop enforces the use of assert_operator(expected, :<, actual) over assert(expected < actual).

# bad
assert(expected < actual)

# good
assert_operator(expected, :<, actual)

Minitest/RefuteOperator cop

This cop enforces the use of refute_operator(expected, :<, actual) over refute(expected < actual).

# bad
refute(expected < actual)

# good
refute_operator(expected, :<, actual)

---

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• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
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• Squashed related commits together.
• Added tests.
• Ran bundle exec rake default. It executes all tests and runs RuboCop on its own code.
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[GUI]

@koic: Is it intentional that this triggers for hash access too? I understand the benefits for math operators like in these examples and in the style guide, but these suggestions for hashes seem less idiomatic to me:

[Correctable] Minitest/RefuteOperator: Prefer using refute_operator(response.headers, :[], "content-length").
    refute(response.headers["content-length"])

[Correctable] Minitest/AssertOperator: Prefer using assert_operator(data["headers"], :[], "authorization").
    assert(data["headers"]["authorization"])

Since I didn't see this type of thing called out in the style guide, I just wasn't sure if this new behavior was intentional or not. Thanks!

[flavorjones]

@GUI you may be interested in #264

[koic]

I've released 0.32.2 with that change. Thank you!
https://github.com/rubocop/rubocop-minitest/releases/tag/v0.32.2

[TSMMark]

This is awesome thanks so much @koic for adding this!

I just ran this across our codebase and discovered an autocorrect which I found interesting:

refute(something == something_else)

corrected to:

refute_operator(something, :==, something_else)

, which is expected, of course.

However, I'm surprised the Minitest/RefuteEqual cop didn't already report this, and correct to:

refute_equal(something, something_else)

Is that a missing feature of Minitest/RefuteEqual? If so, would you like me to open an issue?

Thanks again

[koic]

Thank you for the feedback. I've opened #265. After this I'll open a PR that will make some more adjustments.