First, you'll need to install both the JavaScript and Clojure dependencies, available on NPM and Clojars respectively.
This document assumes you already have a ClojureScript project created and working, with deps.edn or similar, probably a package.json file, etc., and some basic JavaScript and Clojure project setup knowledge.
Install jest-preset-cljest as a dependency:
npm i --save-dev jest-preset-cljest
Add com.pitch/cljest to your deps.edn:
{:deps {com.pitch/cljest {:mvn/version "<VERSION>"}}}cljest works on the same principle as Jest and believes that things should work great by default. With this in mind, cljest will by default either infer from your environment or have something sensible for its configuration values.
More concretely, cljest by default will look for ClojureScript files that have a namespace that ends with -test (files that end in _test.cljs) in the directories that appear in your classpath (for example, src, test). If this is how your project is laid out too, you probably don't need to configure anything yourself!
However, if, for example, you have paths in your classpath that cause unexpected tests to show up in Jest, you use a different namespace for tests, or you generally have a need for a more complex setup, please see our configuration docs for details on how to setup a custom cljest.edn config file.
Unlike the Clojure side of things, you do need to configure Jest, as we're doing something that's a bit different than the default.
To that end Jest with cljest requires a jest.config.js config file. In this configuration file you'll need to at minimum add jest-preset-cljest as your preset and make sure that a setupFilesAfterEnv entry is present.
Create a jest.config.js file and add the following values:
module.exports = {
// The preset you installed earlier, which allows Jest to work with `cljest` and ClojureScript files
preset: 'jest-preset-cljest',
// A setup file for loading CLJS specific things like `is`
setupFilesAfterEnv: ['jest.setup.js'],
}Jest also needs a setup file. This setup file runs before each of your tests.
Create a jest.setup.js file, and add the following code so that you load your configured setup-ns namespace:
const { loadSetupFile } = require("jest-preset-cljest/utils");
loadSetupFile();You don't need to do anything else here. If you need some custom setup, you can configure it in your cljest.edn setup-ns namespace instead (see the configuration docs for more info).
Once you've configured everything, you're almost good to go!
First, you'll need to add a test file. Jest is smart enough to not try to do anything until it finds a test, so make a file with a namespace suffix that matches your config. It's okay that it's empty, since it's only meant to make Jest attempt to run.
Next, start the cljest watch process by calling clj -X cljest.compilation/watch from your project root directory. When started it will start compiling the tests it finds.
While that's starting, you can start Jest by running ./node_modules/.bin/jest. Jest will automatically wait until the server starts and initial compilation is complete before continuing.
If you get an error related to no tests existing in your file, and you got a successful compilation in the cljest watch process, that means your setup is working! Now you're ready to write your first test in Jest 😎
Please see our troubleshooting docs for some possible help, and if you still have issues, please open an issue.