rack-test VS minitest-rails

In this part, we’ll set up our testing environment so that we can test our Rails API using minitest with minitest/spec. We’ll look at the differences between traditional style unit tests and spec-style tests, or specs. I’ll demonstrate why you should use minitest-rails. We’ll look at using rack-test for testing our API. We’ll even create our own generator to generate API specs.

The "app-as-function" has some very concrete applications though, even outside languages like Haskell. The [rack-test](https://github.com/rack/rack-test) gem (and similar languages) work exactly like this: they run the "app" part without the "web server" part to enable much easier testing. Rack middlewares similarly treat the enclosed app as just a function taking some specified input and returning some output value.

How do we tell minitest/spec which test class to use? The tldr is to use the minitest-rails gem. I highly recommend adding the minitest-rails gem to your project. The gem does a lot to integrate the Rails testing ecosystem with Minitest, particularly spec-style tests. One primary benefit is that it configures specs to use ActiveSupport::TestCase or one of its subclasses as the spec’s test class, depending on what is passed describe.