elm-test-bdd-style

BDD style matchers on top of elm-test and elm-check

Getting started

First, follow the getting started steps from the elm-test package.

Then, install elm-test-bdd-style:

elm package install rogeriochaves/elm-test-bdd-style

To use it, just import it on your test:

import ElmTestBDDStyle exposing (..)

Usage example

-- Example.elm
module Example where

import ElmTestBDDStyle exposing (..)

tests : Test
tests =
  describe "Example Text"
    [ it "does math correctly" <|
        expect (1 + 1) toBe 2

    , it "does not miscalculate things" <|
        expect (2 + 2) notToBe 5

    , it "compares two numbers" <|
        expect (10 > 5) toBeTruthy

    , it "exemplifies more complex test cases" <|
        let
          expression = 2 + 2
        in
          expect expression toBe 4
    ]

Right now, elm-test-bdd-style comes only with toBe, notToBe and toBeTruthy, but it is very easy to create your own matchers:

toBeGreaterThan : comparable -> comparable -> Assertion
toBeGreaterThan a b = (a > b) |> toBeTruthy

tests : Test
tests =
  describe "Custom matchers"
    [ it "compares two numbers" <|
        expect 10 toBeGreaterThan 5
    ]

Property Based Testing

You can also lean on the power of elm-check in an idiom-concise way.

First, check-out elm-check page for installing it on your project, you will need the Investigators.

Now just import Check.Investigator and you are good to go:

import ElmTestBDDStyle exposing (..)
import Check.Investigator exposing (..)

tests : Test
tests =
  describe "Property Based Testing"
    [ itAlways "ends up with the same list when reversing twice" <|
        expectThat
          (\list -> List.reverse (List.reverse list))
        isTheSameAs
          (identity)
        forEvery
          (list int)
    ]

And you will get a hundred runs:

You can easily mix those tests with the regular ones inside your describe.