pundit-matchers | RSpec matchers for testing Pundit authorisation policies | Authorization library

The reason why you get a test_helper.rb file instead of an spec_helper.rb file is because rails comes with Minitest as the default framework to write the tests, on the other hand rails has the possibility to use other testing frameworks as Rspec installing it as you mentioned.

In the case, for example of https://github.com/chrisalley/pundit-matchers it says that is a set of RSpec matchers for testing Pundit, so in this case you need to use Rspec in order to use this matchers. If you want to keep using Minitest you probably have to look to a similar option of matchers but for Minitest.

Wether if Rspec or Minispec is better depends on the different aspects of the project and the organizations but both options are powerful options to write tests.

There are more articles in Stack Overflow related to the configuration in Rspec and Minitest, for example:

How is spec/rails_helper.rb different from spec/spec_helper.rb? Do I need it?.

You can also take a look at the documentation for both Rspec and Minitest.

There are also tools to transform your Minitest files to Rspec files like:

https://github.com/jaredbeck/minitest_to_rspec