How to run tests after compile webpack

October 27, 2018

The problem

I'm using webpack for compiling and bundling in one hand. In the other hand I'm using jest for testing.

I want to run the tests after each time that any file was changed (and compiled).

The solution

The solution has 3 steps of modifications the webpack.config.js file:

  1. Add the tests entry
  2. Answer the question How to run a code on each file changing in webpack?
  3. Call for running the tests

Step 1

Add an entry:

1entry: {
2 // ...
3 // add this to let webpack watch on the test files changes
4 tests: "./test/path-to-the-tests-entry.js"
5}

Step 2

To extend the functionality of webpack we can use a plugin. For our usage we can simply add it directly to the plugins section. The only method we should implement in our plugin is apply. In this method we will register to afterCompile hook so in each compile we will run our code.

1plugins: [
2 {
3 // add a custom webpack plugin. For more info: https://webpack.js.org/concepts/plugins/
4 apply: compiler => {
5 // add a hook to run a callback after each compile
6 compiler.hooks.afterCompile.tap('jest', compilation => {
7 // in this part we will run the tests
8 }
9 }
10 }
11]

Step 3

Run

1spawn('npm', ['test'], {stdio:'inherit'});

I'm using spawn and {stdio:'inherit'} to keep the original colors which the terminal should use. (Thanks for the answer: https://stackoverflow.com/a/20145153/863110)

And all togather:

1const { spawn } = require("child_process")
2
3module.exports = {
4 entry: {
5 // ...
6 // add this to let webpack watch on the test files changes
7 tests: "./test/path-to-the-tests-entry.js",
8 },
9 // ..
10 plugins: [
11 {
12 // add a custom webpack plugin. For more info: https://webpack.js.org/concepts/plugins/
13 apply: compiler => {
14 // add a hook to run a callback after each compile
15 compiler.hooks.afterCompile.tap("jest", compilation => {
16 // run `npm test` using `spawn` to keep the format of the terminal just like you run it manually.
17 // for more info: https://stackoverflow.com/a/20145153/863110
18 spawn("npm", ["test"], { stdio: "inherit" })
19 })
20 },
21 },
22 ],
23}
© 2021 - Moshe Feuchtwander