This is the first in what I expect to be an ongoing series of posts on common sources of test flake. Today: Chrome! Specifically, sometimes clicking a link in end-to-end tests, even on a static page, doesn’t navigate to the next page. In the screenshot grabbed from the failing test it might even show the link as outlined as if it had been clicked. There was a period where roughly half of our builds were failing due to this issue, which, as you might imagine, can make you start questioning the value of end-to-end tests.

The Diagnosis

My understanding is that Chromedriver figures out where the element is, then clicks at those coordinates. If the layout shifts in that window, the click can land in the wrong spot. My best guess at what we saw: the mousedown landed on the link, focusing it, but by the mouseup the link had moved, so the two never registered as a real click. Chromedriver has a page on click issues, but it doesn’t seem to be a priority for them to fix.

The Fix

Switch to Firefox with Geckodriver. Maybe a bit cheeky, but that was our solution, and the amount of flake in our end-to-end tests plummeted. You might also consider checking out Cuprite if you’re in Ruby land, as it doesn’t use Chromedriver. There are a number of hackier alternatives, such as retrying the click or doing a JavaScript click() directly on the element, but I’d be concerned about those masking other issues.