Minor cleaning setting up tests

[epergo]

We use minitest for Sinatra's test suite but we weren't using its rake task. I've updated the Rakefile to require and use Minitest default rake task to simplify.

Another change is to rename the helper.rb file to test_helper.rb because I think that name is used more in the community and require it directly without calling File.expand_path

[dentarg]

Should we do require_relative 'test_helper' instead?

[epergo]

I used require because it's the one I've found in other projects (Rails, Pay) and because is what rubygems use when creating a new gem.

The only issue I could think of is that running tests manually from inside the test folder (or any other place different from the root path) won't work, as it won't find the file.

Do you foresee any other issue for not using require_relative?

[dentarg]

Those were the issues I was thinking about. The code before could handle those scenarios, right?

I also recall reading relative being faster.

[dentarg]

See also puma/puma#2902, puma/puma#2964

[epergo]

Enough arguments 😄 updated to use require_relative instead