I don't foresee any problems with allowing both. When I was testing the cukes for specific syntaxes, I found that requiring `:test_unit` loads minitest anyways. I confirmed this in Ruby: https://github.com/ruby/ruby/blob/3603063e4385c45db103d979311f689e9146383e/lib/test/unit/assertions.rb#L7

I'll add a cuke showing they work together.