I encountered the following head-scratcher when trying to run the following RSpec test on MacOs:

➜ bundle exec rspec ./spec/features/some_spec.rb:12
...
Capybara starting Puma…
Version 4.3.8 , codename: Mysterious Traveller
Min threads: 0, max threads: 4
Listening on tcp://127.0.0.1:63422
...
Selenium::WebDriver::Error::WebDriverError:
unexpected response, code=500, content-type="text/html"
Host header or origin header is specified and is not whitelisted or localhost.

After much fruitless poking around in ./spec/rails_helper.rb, I checked my /etc/hosts file and realised I had mapped 127.0.0.1 to a custom name. I updated /etc/hosts to include only the following lines:

127.0.0.1 localhost
0.0.0.0 my.localdev

And hey presto, Selenium would now run the rest of my (still failing) tests.

As an aside, I tried passing the options '--headless', '--disable-web-security', '-–allow-file-access-from-files', '--allowed-origins=*‘ to Capybara in ./spec/rails_helper.rb, and none seemed to have any effect.