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elm-verify-examples Build Status

Verify examples in your docs.

ℹ️ This was formerly known as elm-doc-test.

⚠️ This is not a replacement for tests, this tool should be used for improving your documentation.


$ npm i elm-test -g
$ npm i elm-verify-examples -g
$ elm-test init


$ touch tests/elm-verify-examples.json

elm-verify-examples.json contains information on which files contain verified examples and where to find them.

  "root": "../src",
  "tests": [

It's recommended to add ./tests/VerifyExamples to your .gitignore.

Writing Verified Examples

Verified examples look like normal code examples in doc-comments.
Code needs to be indented by 4 spaces. You can specify the expected result of an expression, by adding a comment --> (the > is important) and an expected expression.

{-| returns the sum of two int.
    -- You can write the expected result on the next line,
    add 41 1
    --> 42
    -- or on the same line.
    add 3 3 --> 6
add : Int -> Int -> Int
add =

Multiline Examples

You can write examples on multiple lines.

{-| reverses the list
        [ 41
        , 1
    --> [ 1
    --> , 41
    --> ]
    rev [1, 2, 3]
        |> toString
        |> String.concat
    --> "321"
rev : List a -> List a
rev =


You can specify imports, if you want to use a module or a special test util.

    import Dict
    myWeirdFunc (Dict.fromList [(1, "a"), (2, "b")]) [2, 1]
    --> "ba"

Intermediate Definitions

You can use intermediate definitions in your example. :information: Unused functions don't get added to the test. This is useful if you wanna add incomplete examples to your docs. ⚠️ Intermediate definitions need a type signature!

    isEven : Int -> Bool
    isEven n =
        n % 2 == 0
    List.Extra.filterNot isEven [1,2,3,4] --> [1,3]
filterNot : (a -> Bool) -> List a -> List a

Types in Examples

You can define union types and type aliases in your examples.

{-| With a union type in the example.
    type Animal
        = Dog
        | Cat
    double Dog
    --> (Dog, Dog)
double : a -> (a, a)
double a =
    (a, a)
{-| With a type alias in the example.
    customTypeAlias defaultUser "?"
    --> "?Luke"
    type alias User =
        { id: Int -- ID
        , name: String
    defaultUser : User
    defaultUser =
        { id = 1
        , name = "Luke"
    customTypeAlias defaultUser "_"
    --> "_Luke"
customTypeAlias : { a | name : String } -> String -> String
customTypeAlias { name } prefix =
    prefix ++ name

Verify Examples

elm-verify-examples only converts your verify-examples into elm-tests. You have to use elm-test in order to run them.

$ elm-verify-examples

By default the first command creates the tests at tests/VerifyExamples/. If you want to have them at a custom location use the --output argument (e.g. elm-verify-examples --output my/custom/path/ will create the tests at my/custom/path/VerifyExamples/).

Also by default the first command looks for the config file at tests/elm-verify-examples.json. If you want it to load a specific config file use the --config argument (e.g. elm-verify-examples --config my/custom/path/elm-verify-examples.json will read the config from my/custom/path/elm-verify-examples.json).

You can run elm-verify-examples for one or more modules explicitly. They don't have to be specified in tests/elm-verify-examples.json.

$ elm-verify-examples ./src/Foo.elm ./src/Foo/Bar.elm

You can pass a custom path to elm-test if necessary.

$ elm-verify-examples --elm-test=./node_modules/.bin/elm-test
# or add it to your elm-verify-examples.json `elmTest: "../node....` 
# you can also pass arguments to elm-test with --elm-test-args 

It will use the elm-test installed with this package.


You can run the examples using:

npm start