Eliminate minitest warnings

https://github.com/seattlerb/minitest/commit/9a57c520ceac76abfe6105866f8548a94eb357b6#L15R8
remove code duplication
Merge pull request #10725 from neerajdotname/remove_code_duplication

Remove code duplication
Merge pull request #10667 from rubys/minitest-autorun

Eliminate minitest warnings
Require only minitest.

minitest/autorun required minitest/spec and we are avoiding to require
it.
Add CHANGELOG entry for 99860582b2b1c0fc42bf84c52aac57b243d42678