Kotest and JUnit with IntelliJ or: don’t frak up your toolchain upgrades

My team and I recently decided to use Kotlin for new features in our existing project. It was a great choice to implement a new authentication process and we’re now rewriting some older parts of the application from Java to Kotlin.

Actually I wanted to use Kotlin for a while now, but there were only minor tasks within the Java part of the project. That finally changed and we can focus to improve the Java backend drastiscally.

Part of this process was a library update. We decided to upgrade JUnit from 4 to 5. A big pain in the ass. I don’t think, I would do it again. JUnit 5 was also part of a bigger problem, even if it was actually PEBCAC.

Kotest and MockK features

If you already know about Kotest or want to know more about the problem I had, just skip to next headline. The Kotest introduction is a little bit longer.

As I dived more and more into Kotlin, I stumbled over a Kotest. A really neat testing framework for Kotlin. There’s nothing wrong with JUnit, but Kotest gives you way more awesome ways to structure your tests.

A little example:

package io.webcodr.demo

import io.webcodr.demo
import io.kotest.assertions.throwables.shouldThrow
import io.kotest.core.spec.style.FunSpec
import io.mockk.*

class UserServiceTest : FunSpec() {
    private val userRepository = mockk<UserRepository>()
    private val service = UserService(userRepository)
    private lateint var user: User

    init {
        beforeTest {
            user = User(1, "Jane", "Doe", "jane@doe.com")

        afterTest {

        context("getUser()") {
            fun verifyRepoCalls() {
                verify {


            test("should succeed") {
                every {
                } returns user



            test("should fail") {
                every {
                } throws UserNotFoundException()

                shouldThrow<UserNotFoundException> {


Kotest offers serveral different styles to write tests. I chose the FunSpec style for this example. You could also use a BDD-like or Jasmine-like style, if you want to.

It’s much more intuitive to nest tests with Kotest. To be fair, JUnit 5 allows you to use @Nested with an inner class to acomplish nesting as well, but it’s not as intuitive and harder to read than trailing lambdas.

Assertions are also a little easier to write. Kotest has over 100 different matchers. You can use them as extensions functions, like in the example above or alternatively as infix functions, for example service.getUser(1) shouldBe user. It’s also quite simple to write custom matchers.

There are many more features like soft assertions, tagging, easy temporay file creation or handling for non-deterministic test cases.

For mocking we decided to use MockK, since it’s way more intuitive to use than Mockito with Kotlin. Don’t get me wrong, Mockito is a great library, but it has one flaw: the when method. when is a keyword in Kotlin and to use it with Mockito, you need to write it in backticks. That’s quite ugly and not intuitive at all.

So, in summary, Kotest offers a bunch of pretty neat features and is very intuitive to use. Of course, JUnit can achieve much of this as well, it’s just not that shiny and little harder to read.

The actual problem or: why the frak is there IntelliJ in the title?

If you migrate an old codebase to Kotlin and want to use Kotest, you will have no choice and have to use JUnit and Kotest in coexistence.

That shouldn’t be a problem, since Kotest uses the JUnit 5 Jupiter engine under the hood. But …

As I wrote a new service in Kotlin and some tests with Kotest, I could not start the JUnit tests anymore. As soon as the maven depedency of Kotest was present, IntelliJ didn’t recognize JUnit tests and used the Kotest files only. With mvn test (Maven Surefire) everything worked fine.

I tried several things and was ready to give up. Search engines didn’t find anything about this problem. Nothing on GitHub, nothing on Stack Overflow.

I hate to give up, so I decided to create a small demo project to open a GitHub issue. Well, that didn’t work out as intended, since the discovery of JUnit tests in the demo project worked fine. The IntelliJ JUnit runner did what it was supposed to: run JUnit and Kotest.

Well, frak. There must be some kind configuration problem with my real project. I already looked at the IntelliJ runner config, Maven files etc. — nothing worked.

I compared the Maven files from both codebases and there was one difference: my real project did not include the JUnit Jupiter Engine depedency. Bingo. I added to the Maven file and guess what? It worked like a charm.

What an embarassment. As we upgraded from JUnit 4 to 5, we forgot to add the new depedency for the engine. I don’t know why the tests worked at all, but it seems the engine is not really necessary for all cases. But it can screw up test discovery quite well, if you forget it.

The dependency configuration in POM file should like this:


Well, that was a long post, but IMO it was necessary to show how this problem came to be and even if you have no trouble at all, perhaps you’ll consider to use Kotest. It’s awesome!


I’m not sure, but this issue could happen with Gradle as well, when you are migrating to JUnit 5.

macOS Catalina EDID Override AKA HDMI color fix

HDMI connections from your Mac to monitor can be a pain in the ass. There is a chance that macOS will detect your monitor as a TV and set the color space to YCbCr. You will get wrong colors and sometimes blurry fonts.

If you’re having this problem, like me, you know the fix: a patched EDID created with this little Ruby script.

The installation of this EDID override could be tedious since the release of El Capitan, as SIP won’t let you access the necessary system files. Just disable it in recovery mode, copy the file and enable it again. Sucks, but works just fine.

Now, Catalina is out for a few hours and has a new way to annoy people who need EDID overrides. All system-related directories and files are read-only, regardless of the status of SIP.

Fortunately Apple was not crazy enough to disable the write access completely.

Help is on the way, ETA 0 seconds!

  1. Patch your EDID
  2. Boot into recovery mode with CMD+R
  3. Login with your user
  4. Open Disk Utility, select your volume (in most cases Macintosh HD) and mount it with your password (yes, again)
  5. Close the Disk Utility and open a Terminal window
  6. Copy the directory with the patched EDID to /Volumes/$VOLUME_NAME/System/Library/Displays/Contents/Resources/Overrides
  7. Reboot and enjoy the right colors again

Here’s an example of the shell commands:

cd /Volumes/Macintosh\ HD/System/Library/Displays/Contents/Resources/Overrides
cp -rf /Volumes/Macintosh\ HD/Users/webcodr/DisplayVendorID-5a63 .

Don’t forget to use the correct volume and user names!

Dear Apple

Just add a simple solution to select the HDMI color space. A simple shell commando with sudo would suffice or at least let us use an override directory within the user library as it was possible many years ago. It just sucks to do this after every macOS upgrade and every time you improve system security, it gets harder.

Please, don’t forget us powers users …

Hello, Dark Mode

Dark mode for Android and iOS? Hold my beer …

It’s quite simple to implement. Every modern browser can evaluate media queries in JavaScript with window.matchMedia() and supports CSS variables.

I added the following to my application JavaScript file:

const preferColorSchemeResult
  = window.matchMedia('(prefers-color-scheme: dark)')

if (preferColorSchemeResult && preferColorSchemeResult.matches === true) {
  document.documentElement.setAttribute('data-theme', 'dark')
} else {
  document.documentElement.setAttribute('data-theme', 'light')

The script will set the data attribute theme on the document element (html) with the possible values dark or light depending on the result of the media query.

There’s no need for a polyfill, even IE 10 supports window.matchMedia()

Stylesheet changes is even simpler, since I already had introduced SCSS color variables a while ago. I just had to replace them with CSS variables.

// colors
$c_white: #fff;
$c_dark-grey: #4A4A4A;

:root {
  --container-background-color: #{$c_white};

[data-theme="dark"] {
  --container-background-color: #{darken($c_dark-grey, 20%)};

That’s basically it. If you use SCSS, please take notice to use interpolations to map the SCSS variables to CSS variables. This change in SassScript expressions was necessary to provide full compatibility with plain CSS.

Since the theme selection is fully automated, I will provide a toggle possibiliry in a future release for those of you who prefer the light mode. This can be easily achieved with a flag in local storage and some minor changes in the JavaScript part.

Snapshot Tests With Jest

Writing tests can sometimes be a tedious task. Mocks and assertions can be a pain in the ass. The latter is especially nasty when HTML is involved. Give me the second p element from the 30th div within an article in aside etc. – no thanks.

The creators of Jest (Facebook) have found a better way: Snapshot tests!

How does it work?

Take a look the following assertion:

it('should create a foo bar object', () => {
  const result = foo.bar()

toMatchSnapshot() takes what ever you give to expect(), serializes it and saves it into a file. The next test run will compare the expected value to the stored snapshot and will fail if they don’t match. Jest shows a nicely formatted error message and diff view on failed tests.

This is really useful with generated HTML and/or testing UI behaviour. Just call the method and let it compare to the snapshot.

Updating snapshots

You added something to your code and the snapshot has to be updated? No problem:

jest --updateSnapshot

If you’re using the Jest watcher it’s even simpler. Just press u to update all snapshots or press i to update the snapshots interactively.

What about objects with generated values?

Here’s an example with an randomized id:

it('should fail every time', () => {
  const ship = {
    id: Math.floor(Math.random() * 20),
    name: 'USS Defiant'


The id will change on every test run, so this test will fail every time. Well, shit? Nope. Jest got you covered:

it('should create a ship', () => {
  const ship = {
    id: Math.floor(Math.random() * 20),
    name: 'USS Defiant'

    id: expect.any(Number)

Jest will now only compare the type of the id and the test will pass.

For certain objects like a date, there is another possibility:

Date.now = jest.fn(() => 1528902424828)

A call of Date.now() will call the mock method and always return the same value.

Some advice

  1. Always commit your snapshots! If they are missing,CI systems will always create new snapshots and the tests will become useless.

  2. Snapshot tests are an awesome tool, but don’t be too lazy. They are no replacement for other assertion types, especially if you’re working test-driven. Rather use them alongside with your other tests.

  3. Write meaningful test names. Well, you heard that one before, didn’t you? Really, it helps a a lot when tests fail or you have to look inside a snapshot file. Jest takes a test name as an id inside a snapshot file. That’s why you have to update a snapshot after changing the name.

Introducing DeliveryGuy

I like the Fetch API. It’s supported by all modern browsers, easy to use and has some really good polyfills for older devices. But Fetch has one major flaw: it will only throw errors if there is a network problem.

That’s a really odd decision from my point of view. Nearly any HTTP library out there throws errors or rejects the promise in case of a HTTP error.

A Fetch response object has the property ok to determine if the server responded with an error, but that’s not very comfortable to use.

Since my team and I have decided to use Fetch in a Vue-based web app, I decided to create a little wrapper for much more convenience. Say hello to DeliveryGuy.


Well, surprise, it’s a Node module, so just use any package manager you like. My personal choice is yarn.

yarn install delivery-guy


import { deliverJson } from 'delivery-guy'

const getItems = async () => {
  try {
    const items = await deliverJson('/api/items')
  } catch (e) {
    console.log('HTTP Status', e.response.status)
    console.log('Response Body'. e.responseBody)

What’s going on here?

DeliveryGuy exports two main functions:

  • deliver() will return a response promise like fetch() does.
  • deliverJson() presumes your response body contains JSON. It’s basically a shortcut and returns the promise of Response.json().

Both will accept the same two parameters as fetch() does and pass them along.

If the server responds with a HTTP error, DeliveryGuy will throw an error.

Due to the inheritance limitations of built-in classes with ES5 I mentioned in my last post, it’s only possible to set custom properties of a custom error class.

DeliveryGuy provides additional two properties on an error object:

  • response has the original response object of a Fetch call.
  • responseBody contains the response body and will try to parse it as JSON. If JSON.parse fails, it will return the response body in its original state.


DeliveryGuy allows you comfortably call the Fetch API without a hassle on HTTP errors. Just use try/catch and you’re done.

Please let me know on GitHub if you have feedback, a feature request or found a bug. Thank you!

Why custom errors in JavaScript with Babel are broken

Have you ever tried to write a custom error class in JavaScript? Well, it does work to a certain extend. But if you want to add custom methods or call instanceof to determine the error type it will not work properly.

Here is a little example of a custom error class:

class MyError extends Error {
  constructor(foo = 'bar', ...params) {
    if (Error.captureStackTrace) {
      Error.captureStackTrace(this, MyError)
    this.foo = foo
  getFoo() {
    return this.foo

try {
  throw new MyError('myBar')
} catch(e) {
  console.log(e instanceof MyError) // -> false
  console.log(e.getFoo()) // -> Uncaught TypeError: e.getFoo is not a function

Works fine in any browser with ES6/ES2015 support, but if you transpile the example with Babel to ES5 and execute the code, you will get the results shown in the comments.


Due to limitations of ES5 it’s not possible to inherit from built-in classes like Error, see the Babel docs.

Possible solution

The docs mention a plug-in called babel-plugin-transform-builtin-extend to resolve this issue, but if you have to support older browsers it may not help. In order to work the plug-in needs support for __proto__. Take a guess which browser does not support __proto__ … and of course, it’s the web developers best friend aka Internet Explorer. Thankfully it affects only version 10 and below.


If it’s not feasable to use the plug-in, you can at least access properties set in the constructor. A call to e.foo in the example is possible, but e instanceof MyError will return false, since you will always get an instance of Error.


Nothing of this ideal. We have to wait until it’s possible to use ES6/ES2015 directly. Yes, we all could set our transpile targets to ES6/ES2015 today, but our clients usually won’t allow it. Some customer is always browsing the web with an ancient device/browser.

Awesome tests with Vue and Jest

Jest is a very neat JavaScript testing library from Facebook. It’s mostly syntax-compatible with Jasmine and needs zero or very less configuration. Code coverage reports are there out-of-the-box and with sandboxed tests and snapshot testing it has some unique features.

Set-up Jest


You are using Vue CLI? Consider yourself lucky, the set-up of Jest could not be simpler:

yarn add --dev jest @vue/cli-plugin-unit-jest
vue invoke unit-jest

Vue CLI will do the rest and also create an example spec for the HelloWorld component.


Install all necessary dependencies:

yarn add --dev @vue/test-utils babel-jest jest jest-serializer-vue vue-jest

Create jest.config.js in your project root directory:

module.exports = {
  moduleFileExtensions: ['js', 'json', 'vue'],
  transform: {
    '^.+\\.vue$': 'vue-jest',
    '^.+\\.js?$': 'babel-jest'
  moduleNameMapper: {
    '^@/(.*)$': '<rootDir>/src/$1'
  snapshotSerializers: ['jest-serializer-vue'],
  testMatch: ['<rootDir>/src/tests/**/*.spec.js']

Please adjust the paths in moduleNameMapper and testMatch to your project.

You should also add a modern JavaScript preset to your .babelrc file:

  "presets": ["es2015"]

Optional step

Add the following line to your .gitignore file:


The set-up is now complete. Let’s write a test file!

Writing tests

Here is a litte example Vue component:

  <ul class="demo">
    <li class="demo__item" v-for="value in values" :key="value">{{ value }}</li>

export default {
  name: 'demo',
  data () {
    return {
      values: []
  created() {
  methods: {
    async fetchValues() {
      const response = await fetch('/api/demo/values')
      this.values = await response.json()

The component Demo will fetch some values after its creation and display them in an unordered list. This is example is quite simple, but testing is a little more complex due to the usage of fetch, async and await.

Of course, there are some tools to help us:

yarn add --dev fetch-mock flush-promises

Now, let’s write a test:

import { shallow } from '@vue/test-utils'
import fetchMock from 'fetch-mock'
import flushPromises from 'flush-promises'
import Demo from '@/components/Demo.vue'

const values = [

describe('Demo.vue', () => {
  beforeEach(() => {
    fetchMock.get('/api/demo/values', values)

  it('renders component', async () => {
    const wrapper = shallow(Demo)
    await flushPromises()


  afterEach(() => {

What’s going on?

  1. shallow from Vue Test Utils creates a wrapper of the rendered and mounted component, any child components will be stubs. If you need child components in your test, please use mount instead of shallow.

  2. fetchMock will create a mocked version of the Fetch API. In this case it will return the defined values for a GET request to /api/demo/values. If you send a request that’s not defined in fetchMock, it will throw an exception and break your tests.

  3. The test itself is defined as async to use await for flushPromises(). It will wait until the mocked request is finished and the values are stored in the component’s data.

  4. You can now access the data property values and compare the content to the response of the mocked HTTP request.


Setting up Jest for Vue is easy, even if you have to do it manually.

A little warning: setting up Jest for an existing app can be tedious. The current AngularJS app of our customer can’t be tested with Jest, at least for now. The AngularJS HTTP mock does not work and I haven’t figured out the problem yet.

But enough of Angular: the real deal comes with the testing itself. Async/await is a nice and simple way for testing asynchronous behaviour. I don’t think this could be easier and it’s a reliable method with the power of modern JavaScript. Try to imagine what the demo test would look like in ES5 …

Vue Loader Setup in Webpack

Since it’s no option to use Vue CLI in my current project, I had to manually add vue-loader to the Webpack config. Well, I was positively surprised how simple it was. Especially compared to a manual set-up of Angular 2 shortly after its launch in late 2016, while Angular CLI was an alpha version and buggy as hell.

Shall we begin?


Let’s add the necessary modules to the package:

yarn add --dev vue-loader vue-template-compiler
yarn add vue

If you want to use a template engine like Pug or prefer TypeScript over JavaScript, you can add the respective Webpack loader package, pug-loader for example. Webpack will also tell you in detail, if modules are missing.


Just add the following rule to your Webpack config:

  test: /\.vue$/,
  use: [
      loader: 'vue-loader'

Webpack will now be able to use import statements with Vue single file components.

If you want to have a separate JavaScript file with your Vue application, you can add a new entry point:

  entry: {,
    'current-application': [
      path.resolve(__dirname, 'js/current-application.js')
    'vue-application': [
      path.resolve(__dirname, 'js/vue-application.js')

Not fancy enough? How about vendor chunks?

  optimization: {
    splitChunks: {
      chunks: 'all',
      cacheGroups: {
        vendor: {
          chunks: 'initial',
          test: /node_modules\/(?!(vue|vue-resource)\/).*/,
          name: 'vendor',
          enforce: true
        'vue-vendor': {
          chunks: 'initial',
          test: /node_modules\/(vue|vue-resource)\/.*/,
          name: 'vue-vendor',
          enforce: true

This will separate your vendor files from node_modules into vendor.js and vue-vendor.js. The property test contains a regex to determine which modules should go into the vendor chunks.

Of course, this comes not even close to what Vue CLI can do. I highly recommend to use Vue CLI when it’s feasible. It’s quite easy to configure while not being dumbed down, has an excellent documentation and is very well maintained. At least for our customer’s set-up it would be difficult to use Vue CLI at the moment, but we are eager to migrate to Vue CLI asap.

Pimp Your Visual Studio Code

Like VS Code? Yeah, me too. Here are some very useful extensions and optical enhancements to get an even better experience with VS Code.


Settings Sync

I love my Mac, but sometimes I have to do stuff (besides gaming) on my Windows PC as well. So, if I want to use the same config on both devices, I have to install my extensions and copy my config back and forth. That sucks. Settings Sync to the rescue! It syncs your settings, extensions etc. through the power of Gists on GitHub.



It’s quite simple: just bookmark certain lines of code you need often.


EditorConfig for VS Code

Share your coding styles between editors, IDEs etc. on a per project basis. It’s really nice for teams as well.


Bracket Pair Colorizer

Bracket madness? No more!


Markdown All in One

Do you write a lot of Markdown? Here are some really useful helpers.




If you like darker and bluish color themes, give Cobalt2 a try. The color choices with a contrast between yellow and blue can reduce strain on your eyes.


Material Icon Theme

Matches nicely with Cobalt2 or other darker themes. There are a ton of icons for almost any file type and even for many special folders like node_modules etc.


But that’s not the end. VS Code can do much more, you can find some other very useful tips and tricks on vscodecandothat.com.

Dear GitHub

Look, I want to like Atom, but there are too many caveats. Atom is slow and resource hungry as hell, which is especially bad on a mobile device. It literally eats my MacBook’s battery away. VS Code is not perfect either, but the general experience is much better. So, please, get your shit together and improve Atom. We need more awesome editors on the market!

Let's Encrypt Wildcard Certificates with acme.sh and CloudFlare

A few weeks ago Let’s Encrypt finally launched ACME 2.0 with support of wildcard certificates. Woohoo!

Wait, what are wildcard certificates?

Wildcard certificates allow you to use multiple hostnames of your domain with one certificate. Without them you need a separate certificate for each host like foo.webcodr.io and bar.webcodr.io. A wildcard certificate can be issued for *.webcodr.io and that’s it. One certificate to rule them all.

Get started

My nginx example used certbot to issue certificates from Let’s Encrypt, but there’s a better tool: acme.sh

Acme.sh is written in Shell and can run on any unix-like OS. Since it’s also installed with a Shell script, there’s no need for a maintained package to get the latest features. Just run:

curl https://get.acme.sh | sh

That’s it. The install script will copy acme.sh to your home directory, create an alias for terminal use and create a cron job to automatically renew certificates.

DNS challenge

To issue a wildcard certificate ACME 2.0 allows only DNS-based challenges to verify your domain ownership. You can manage this manually, but challenge tokens will only work for 60 days, so you have to renew it every time a certificate expires.

Well, that sucks. But acme.sh has you covered. It supports the APIs of many DNS providers like CloudFlare, GoDaddy etc.

The following guide will show you how to use the CloudFlare API to automatically update the DNS challenge token. No CloudFlare? No problem, you can find examples for all supported DNS providers within the ache.sh docs.

Set-up CloudFlare

Login to CloudFlare and go to your profile. You’ll need the global API key.

Set your CloudFlare API key and your account email address as environment variables:

export CF_Key="sdfsdfsdfljlbjkljlkjsdfoiwje"
export CF_Email="you@example.com"

I recommend to put this environment variables into your .bashrc, .zshrc or in the respective file of your favorite shell.

Issue a wildcard certificate

acme.sh --issue --dns dns_cf -d "*.webcodr.io" -w "/what/ever/dir/you/like/*.webcodr.io"

Your new certificate will be ready soon and acme.sh will automatically renew it every 60 days. Just update your web-server configuration to the new path. I recommend also to create a cron-job reloading the web-server every night to load a renewed certificate.

Unclutter your ngnix config

If you manage multiple hosts within the same nginx, you can use include to put your TLS configuration in a separate file to avoid duplicates.

Create a separate file for your TLS configuration

File: /etc/nginx/tls-webcodr.io

ssl_certificate /home/webcodr/.acme.sh/*.webcodr.io/*.webcodr.io.cer;
ssl_certificate_key /home/webcodr/pi/.acme.sh/*.webcodr.io/*.webcodr.io.key;
ssl_trusted_certificate /home/webcodr/.acme.sh/*.webcodr.io/ca.cer;
ssl_session_timeout 1d;
ssl_session_cache shared:SSL:50m;
ssl_session_tickets off;
ssl_protocols TLSv1.1 TLSv1.2;
ssl_ecdh_curve secp384r1;
ssl_prefer_server_ciphers on;
add_header Strict-Transport-Security max-age=15768000;
ssl_stapling on;
ssl_stapling_verify on;

Update your site configuration

File: /etc/nginx/sites-enabled/webcodr.io

server {
  listen 80;
  server_name webcodr.io;

  location / {

server {
  listen 443 ssl http2;
  server_name webcodr.io;
  ssl on;

  include tls-webcodr.io;

  location / {

Repeat this for every site on a host on this domain and reload nginx. And you’re done. Just one certificate and TLS config for all your sites. Pretty neat, huh?