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rtfeldman
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Description

Runs elm-test suites from Node.js. Get it with npm install -g elm-test

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node-test-runner Version

Runs elm-explorations/test suites in Node.js.

When people say “elm-test” they usually refer to either:

  • This CLI tool for running tests.
  • elm-explorations/test – an Elm package for defining tests that this CLI tool can run.

Installation

npm install --save-dev elm-test

Quick start

Install elm-explorations/test and create

tests/Example.elm
:
npx elm-test init

Run tests in the

tests/
folder:
npx elm-test

Run tests in one particular file:

npx elm-test tests/Example.elm

Run tests in files matching a glob:

npx elm-test "src/**/*Tests.elm"

Note: The double quotes are important! Without quotes, your shell might expand the globs for you. With quotes, elm-test expands the globs. This way the watcher can pick up new tests matching the globs, and it will work cross-platform.

Run in watch mode:

npx elm-test --watch

Where to put tests

Locating files containing tests

There are 3 places you could put your tests:

  1. In the

    tests/
    folder.

    This is the default and requires no extra setup.

  2. In any source directory (

    "source-directories"
    in
    elm.json
    for applications,
    src/
    for packages) as separate files.

    A convention is to put test files next to the file it tests with a

    Tests
    suffix. For example, you could have
    src/LoginForm.elm
    and
    src/LoginFormTests.elm
    .

    This requires telling elm-test which folders/files to run. Examples:

    npx elm-test "src/**/*Tests.elm"
    npx elm-test test/frontend/elm
    

    You might also need to configure your editor to understand that the

    "test-dependencies"
    in your
    elm.json
    are available in these files.
  3. In already existing source files.

    This allows testing internal functions without exposing them. (Be aware that testing implementation details can sometimes be counter-productive.)

    This requires moving everything in

    "test-dependencies"
    in your
    elm.json
    into regular
    "dependencies"
    , so your project still compiles. This also helps your editor. Note that this approach isn’t suitable for packages, since you don’t want your package to unnecessarily depend on elm-explorations/test.

You can mix all three variants if you want:

npx elm-test tests "src/**/*Tests.elm" app

In this example,

"src"
and
"app"
need to be in
"source-directories"
in
elm.json
.

Locating tests within files

For elm-test to find tests in your files you need to:

  1. Create top-level values of the type Test. You can name the values anything – the only thing that matters is that their type is
    Test
    .
  2. Expose them.

Example:

module LoginForm exposing (alreadyLoggedInTests, tests)

import Test exposing (Test)

tests : Test tests = -- ...

alreadyLoggedInTests : Test alreadyLoggedInTests = -- ...

Some prefer to expose a single

Test
value and group everything using describe. Some prefer to expose several
Test
values.

Also check out the elm-explorations/test quick-start guide!

Command Line Arguments

These are the most common commands and flags. Run

elm-test --help
for an exhaustive list.

Note: Throughout this section, the

npx
prefix is omitted for brevity.

install

Like

elm install
, except elm-test will install to
"test-dependencies"
in your
elm.json
instead of to
"dependencies"
.
elm-test install elm/regex

init

Runs

elm-test install elm-explorations/test
and then creates a
tests/Example.elm
example test to get you started.

elm-test init
requires an
elm.json
file up the directory tree, so you will need to run
elm init
first if you don’t already have one.

After initializing elm-test in your project, try out the example by running

elm-test
with no arguments.
elm init
elm-test init
elm-test

--watch

Start the runner in watch mode. Your tests will automatically rerun whenever your project changes.

elm-test --watch

--seed

Run with a specific fuzzer seed, rather than a randomly generated seed. This allows reproducing a failing fuzz-test. The command needed to reproduce (including the

--seed
flag) is printed after each test run. Copy, paste and run it!
elm-test --seed 336948560956134

--fuzz

Define how many times each fuzz-test should run. Defaults to

100
.
elm-test --fuzz 500

--report

Specify which format to use for reporting test results. Valid options are:

  • console
    (default): pretty, human readable formatted output.
  • json
    : newline-delimited json with an object for each event.
  • junit
    : junit-compatible xml.
elm-test --report json

--no-color

Disable colored console output.

Colors are also disabled when you pipe the output of

elm-test
to another program. You can use
--color
to force the colors back.

Alternatively, you can set the environment variable

FORCE_COLOR
to
0
to disable colors, or to any other value to force them.

See chalk.supportsColor for more information.

--compiler

If

elm
is not in your
$PATH
when elm-test runs, or the Elm executable is called something other than
elm
, you can use this flag to point to your installation.
elm-test --compiler /path/to/elm

To run a tool installed locally using

npm
you can use
npx
:
npx elm-test

npx
adds the local
node_modules/.bin/
folder to
$PATH
when it executes the command passed to it. This means that if you have installed
elm
locally,
elm-test
will automatically find that local installation.

As mentioned in Installation we recommend installing elm-test locally in every project. This ensures all contributors and CI use the same version, to avoid nasty “works on my computer” issues.

Travis CI

If you want to run your tests on Travis CI, here's a good starter

.travis.yml
:

language: elm
elm:
  - 0.19.1

Here is an example

travis.yml
configuration file for running tests in CI.

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