Selenium: Disable CSS transitions and fail on JavaScript errors

I've done both steps for a second time (in a different project) now, so I thought it is worth a blog post.

1. CSS transitions

If you use CSS animations, you have three choices for your tests:

  1. Sleep for a specific amount of time and hope the animation has finished after
  2. Introduce wait statements to make sure the animation ended
  3. Disable animations

Option 1. was out of the question, sleep statements are just not reliable and bad practice.

I stepped away from 2., because it might be a) a lot of statements which clutter your test and b) there's no out-of-the-box solution provided by Selenium. You'd have to write your own hacky one.

So I tried 3.

Some helpful links:

I ended up with this in Kotlin (kotest) using the Testcontainers Selenium solution. Still hacky, but my tests run reliably without the sleep statements now. :)

(chrome is a BrowserWebDriverContainer)

Selenium 3 (with kotest 4):

  override fun beforeTest(testCase: TestCase) {
    driver = EventFiringWebDriver(chrome.webDriver)
    driver.register(object : AbstractWebDriverEventListener() {
      override fun afterNavigateTo(url: String, driver: WebDriver) {
        val disableTransitions =
          "const styleElement = document.createElement('style');styleElement.setAttribute('id','disable-transitions');const styleTagCSSes = document.createTextNode('*,:after,:before{-webkit-transition:none!important;-moz-transition:none!important;-ms-transition:none!important;-o-transition:none!important;transition:none!important;-webkit-transform:none!important;-moz-transform:none!important;-ms-transform:none!important;-o-transform:none!important;transform:none!important}');styleElement.appendChild(styleTagCSSes);document.head.appendChild(styleElement);"
        (driver as JavascriptExecutor).executeScript(disableTransitions)
        super.afterNavigateTo(url, driver)

Selenium 4 (with kotest 5):

  override suspend fun beforeTest(testCase: TestCase) {
    val disableAnimationsListener = object : WebDriverListener {
      override fun afterGet(driver: WebDriver, url: String) {
        super.afterGet(driver, url)
    driver = EventFiringDecorator(disableAnimationsListener).decorate(chrome.webDriver)

2. JavaScript console logging errors

Second thing I wanted to check is that no JavaScript errors occured during the test.

Step one: I enabled logging of all levels, just in case I want to inspect non-errors also:

val loggingPreferences = LoggingPreferences()
loggingPreferences.enable(BROWSER, ALL)

val options = ChromeOptions()
options.setCapability(LOGGING_PREFS, loggingPreferences)
options.setCapability("goog:loggingPrefs", loggingPreferences)

The goog:loggingPrefs is for Google Chrome only, see here.

Update: With Selenium 4 there is now a constant: The previous LOGGING_PREFS from org.openqa.selenium.remote.CapabilityType.LOGGING_PREFS is now deprecated.

Step two: Assert the logs (via kotest again):

fun assertBrowserLogs() {
    val entries = driver.manage().logs().get(BROWSER)
    val warningsAndHigher = entries.filter { it.level.intValue() >= WARNING.intValue() }

    withClue("Browser logs") { warningsAndHigher.shouldBeEmpty() }