Janiczek / elm-common-tests

CommonTests

Test your implementations of common data structures with ease with these predefined tests!

All you need to do is to provide a record with your functions, like:

module Example exposing (..)

import CommonTests
import OpaqueDict
import Test exposing (Test)


suite : Test
suite =
    CommonTests.isDict
        -- Debug.toString
        { dictToString = Debug.toString

        -- Creation
        , empty = Just <| OpaqueDict.empty identity
        , singleton = Just <| OpaqueDict.singleton identity
        , fromList = Just <| OpaqueDict.fromList identity

        -- Updating
        , insert = Just OpaqueDict.insert
        , update = Just OpaqueDict.update
        , remove = Just OpaqueDict.remove
        , map = Just OpaqueDict.map
        , filter = Just OpaqueDict.filter
        , union = Just OpaqueDict.union
        , intersect = Just OpaqueDict.intersect
        , diff = Just OpaqueDict.diff

        -- Querying
        , size = Just OpaqueDict.size
        , isEmpty = Just OpaqueDict.isEmpty
        , member = Just OpaqueDict.member
        , get = Just OpaqueDict.get
        , toList = Just OpaqueDict.toList
        , foldl = Just OpaqueDict.foldl
        , foldr = Just OpaqueDict.foldr
        , partition = Just OpaqueDict.partition
        , keys = Just OpaqueDict.keys
        , values = Just OpaqueDict.values
        , merge = Just OpaqueDict.merge
        }

Whenever your functions don't behave like the ones from elm/core Dict, you'll get failed tests like:

↓ Example
↓ Conformance to elm/core Dict
↓ Creation
✗ empty

Given (({ dict = Dict.fromList [], keyToString = <function> },Dict.fromList []),[UpdateNJJN " "])

    Starting model:

        Tested Dict:   { dict = Dict.fromList [], keyToString = <function> }
        elm/core Dict: Dict.fromList []

    Msgs applied to it (failed a contract):

        [ update " " nothingToJustJustToNothing
        ]

    Resulting model:

        Tested Dict:   { dict = Dict.fromList [], keyToString = <function> }
        elm/core Dict: Dict.fromList [(" ", 1)]

    Failure:


        ╵
        │ Expect.equalLists was shorter than
        ╷
        (" ",1)

This can be interpreted as: "I've started with an empty Dict, tried to run Dict.update " " nothingToJustJustToNothing on it, and got differing results between your Dict and the elm/core Dict: yours stayed empty while the core one has one element."

For more explanation take a look at the isDict function docs.