Rails 4 Minitest minimal setup - ruby-on-rails

Question

I notice after reading the rails guide docs
that minitest comes with the newer Ruby versions out of the box, so it's available right away, no need to install anything else. Rails 4 by default use that.
If fact i use the minitest-reporter gem and it work like charm.
The confusion comes when i see examples defining the :test group of the gemfile like this:
group :test do
gem 'minitest-rails'
gem 'minitest-rails-capybara'
gem 'minitest-colorize'
gem 'minitest-focus'
end
Why is the need of include a minitest-rails gem ?? To use some rails generation later or other kind of specs ??
I'm kinda confused here so any thought about Rails 4 Minitest integration will be appreciated.

Answer 1

According to the mini-test rails README, it makes it so Rails generators for tests will generate in minitest style. It also makes it so minitest style actually works in Rails ActiveSupport::TestCase test classes. (which is what Rails test cases do).
minitest comes with ruby, but the Rails' ActiveSupport::TestCase, which Rails test classes all are, doesn't normally use minitest. minitest-rails makes it so it does.
This project aims to enable Minitest within the Rails TestCase classes. Your test will continue to inherit from ActiveSupport::TestCase, which will now support the spec DSL. You can generate test files with the standard model, controller, resource, and other generators:
https://github.com/blowmage/minitest-rails
One thing that makes this more confusing, is that in newer versions of ruby [i accidentally said 'Rails' before, but it's newer versions of ruby that matter], it's true that Minitest is there and old Test::Unit is not. But Minitest has a sort of "pretend to be Test::Unit" mode -- that's what Rails ActiveSupport::TestCase ordinarily uses, the old Test::Unit style of testing -- even if it's actually the minitest library providing it. minitest-rails makes it support the newer Minitest::Spec::DSL style.

Answer 2

minitest-rails is already a dependency of minitest-rails-capybara which you are using and have added to the test group.
So regardless of whether you explicitly add minitest-rails to the Gemfile or not, it will be installed for your application. However, you might wish to explicitly specify a specific version of minitest-rails that you want to use, and in such case you should add the gem to your Gemfile with the wanted version (something you are not doing in your code).

Answer 3

If you have no interest in using Minitest's spec DSL then you don't need to include minitest-rails. If you have no interest in Capybara's spec DSL then you don't need to include minitest-rails-capybara, although if you want to use Capybara you will need some other mechanism to add it to your application. The minitest-capybara gem doesn't do any rails integration.
It is possible that these two libraries are added to add the Capybara support even though you use test style tests and not spec style tests. The minitest-rails-capybara gem adds generators for Capybara tests in both test style and spec style. Try git blame on your Gemfile to find the commit where those two lines were added, as the commit message might explain why they are in the application.