Do you use the chromedriver-helper gem? How about Capybara? Have you seen this error Selenium::WebDriver::Error::UnknownError: unknown error: call function result missing? If so then keep reading for how I fixed it for my local development.

chromedriver-helper enables a dead simple process for using headless Chrome with Capybara. Recently, we upgraded to using it for our feature spec suite. Unfortunately, after switching away from Poltergeist I started noticing errors the looked like this:

  unknown error: call function result missing 'value'
    (Session info: headless chrome=72.0.3626.119)
    (Driver info: chromedriver=2.31.488763 (092de99f48a300323ecf8c2a4e2e7cab51de5ba8),platform=Linux 4.4.0-142-generic x86_64)

So what the heck does this mean?

My first thought was because I’m running Elementary OS which is based off of Ubuntu 16.04, that I had come up against an incompatibility between my OS and the gem. Luckily, my second thought was to check the different versions listed in the error message.

headless chrome=72.0.3626.119

Checking chrome://settings/help told me that I was indeed running 72.0.3626.119. Which brings me to the first action I took.

Update Chrome

I found out after downloading the 64-bit .deb package that the latest version of chrome was 72.0.3626.121. Just a few versions out of date between .121 and .119. Still worth a shot.

So step 1, I updated Chrome from the following link. Next I relaunched and double checked Chrome’s settings to confirm the update had been made.

Unfortunately, the same spec failure persisted.

Update chromedriver

I use asdf locally as my package version manager. So when I checked which chromedriver it told me that it lived within the /home/josh/.asdf/shims/chromedriver directory. At this point I tried a couple different things to install the newest version but all of them failed. I was able to determine that the version I was using 2.31.488763 was out of date with the latest 2.46 by running the following cURL command: curl -sS

Alright, so we’re getting somewhere here. Looks like our version is still out of date. Hmm… That’s when I thought, “maybe I should read the documentation for chromedriver-helper”. Which led to the following section Updating to latest chromedriver. Duh.

Basically the way to update chromedriver helper is via a command:


This finally upgraded my chromedriver version to ChromeDriver 2.46.628388 (4a34a70827ac54148e092aafb70504c4ea7ae926). Going back to the feature spec I tried running them again and success! They worked! Well, the specs still failed but chromedriver was no longer to blame. Time for some red-green-refactor

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