Testing on the Elm track

Learn how to test your Elm exercises on Exercism

Tests for an Elm project live in the tests/ subdirectory of that project. Each exercise tests suite can be run from that exercise root directory.

$ cd ~/exercism/elm/hello-world
$ elm-test

Watch for Changes

Automatically run tests again when you save changes:

$ elm-test --watch

Test Driven Development Flow

In most exercises, tests are already written in the file tests/Tests.elm. Your goal is to make them pass by writing the code required in the src/<exercise>.elm file. Focus on the first failing test, fix it, then remove or comment the next skip <| snippet in the tests file and repeat until all tests pass.

Feeling Stuck?

Your first goal is to get your code to compile, even with Debug.todo in it. If you feel you don't know how to do something, it is often useful to extract that piece into its own unimplemented function.

complexOperationOnMultipleStrings : List String -> List String
complexOperationOnMultipleStrings allStrings =
    List.map complexOperation allStrings

complexOperation : String -> String
complexOperation input =
    Debug.todo "Extracted operation into its own function"

Adding a type annotation on this extracted function will both help your thinking and the compiler to give you better error messages.

Cleaning up your code

Consider running elm-format on your code before submitting it and even setting it up in your text editor for automatic formatting on save.