6.0.3 • Public • Published

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


There is no need for any configuration. elm-verify-examples will run on all elm files in the specified source-directories (elm.json). It's possible to create a config file if you want to run it on only a subset of files or on additional markdown files.

$ touch tests/elm-verify-examples.json

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

  "tests": ["Mock", "Mock.Foo.Bar.Moo", "./README.md"]

Alternatively you can run elm-verify-examples on all elm files in your source directories:

  "tests": "all"


  "tests": ["all", "Some.md"]

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

If you are building a package, you can pass the string "exposed" instead of an explicit list of modules, this will cause all the documented modules in your package to be verified. This makes it easier to keep these in sync.

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]
        |> List.map 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. :warning: Intermediate definitions need a type signature!


    isEven : Int -> Bool
    isEven n =
        remainderBy 2 n == 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

Examples in markdown files

You can also verify code example in markdown files (such as your README). To do so, add the file's path to your elm-verify-examples.json file and write your example using the sames rules as above (no need for 4-space indentation here).

This is my README!
It explains how the `Documented` module works:

import Documented

Documented.two --> 2

Verify Examples

elm-verify-examples converts your verify-examples into elm-tests, and optionally runs them using elm-test. To only generate the test files in tests/VerifyExamples/:

$ elm-verify-examples

This is useful if you want to run your tests using different runner than elm-test, e.g. elm-coverage. If you also want to run the generated tests:

$ elm-verify-examples --run-tests

Note that this way the test files will be removed after they are ran.

By default, this 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.

Package Sidebar


npm i elm-verify-examples

Weekly Downloads






Unpacked Size

141 kB

Total Files


Last publish


  • rtfeldman
  • schtoeffel
  • eeue56