For ruby, minitest information can be found here:
main: https://github.com/seattlerb/minitest
docs: http://docs.seattlerb.org/minitest/
In rails, minitest is kind of an extension of the ruby minitest suite:
main: https://github.com/blowmage/minitest-rails
docs: http://blowmage.com/minitest-rails/
Interesting links:
http://chriskottom.com/blog/2014/10/4-fantastic-ways-to-set-up-state-in-minitest/
http://tenderlovemaking.com/2015/01/23/my-experience-with-minitest-and-rspec.html
https://thomascannon.me/posts/porting-to-minitest-part-2/
https://github.com/metaskills/minitest-spec-rails
Other stuff to check:
https://github.com/thoughtbot/shoulda
https://github.com/freerange/mocha
http://brakemanscanner.org/docs/
http://sam-koblenski.blogspot.com.br/2014/06/rspec-or-minitest-how-does-one-choose.html
https://github.com/koblenski/sample_app_rails_4
http://buildingrails.com/a/rails_functional_testing_controllers_for_beginners_part_1
http://blog.crowdint.com/2013/06/14/testing-rails-with-minitest.html
https://ariejan.net/2015/04/07/testing-with-minitest/
https://www.railstutorial.org/book/modeling_users#sec-a_validity_test
test/
test_helper.rb
controllers/
fixtures/
helpers/
integration/ <- Capybara tests go here
mailers/
models/
unit/lib/ <- Tests for your /lib code