applied-fp-course/level04

Level 04

We're going to add some tests to our application! Types are awesome, tests are pretty good. Types AND tests is pretty much perfect.

These tests will not be awe inspiring, this exercise is primarily to introduce you to adding tests to your Haskell application. The setup of the Cabal file is already completed for you, but will be covered.

As is to be expected, there are multiple testing frameworks and packages available but we will only cover one here. We will use the HSpec framework, with the hspec-wai package to make our lives a bit easier.

Start in tests/Test.hs.

Aside: Tool Introduction - ghcid

Additionally we'd like to introduce a command line tool that we find quite useful for Haskell development; ghcid. This is a very lightweight tool that works for any project with a functioning cabal setup.

If you would like to use it, consult its documentation for how to install it, and then in an spare open terminal window, navigate to the root of the Haskell project and run $ ghcid.

It will then attempt to build your project, if errors are found they will be displayed. But more importantly you can go back to editing files in the project and ghcid will refresh in the background. Providing you with new error messages or All Good if it cannot find any errors.

ghcid provides extremely fast feedback, allowing for a nice development process with constant feedback about your changes. It is very useful in tandem with type holes. Give it a try!