One issue that we see a lot in support here at CircleCI is flaky web browser tests. Since most browser automation frameworks use Selenium under the hood, I decided to sit down and see what was needed to get better logs of the test process to aid customers in troubleshooting their hung and failed builds.
None of the webdriver browser testing frameworks appear to have very good logging when things go wrong. It seems that at best you will get a failed test due to the test not finding an element you know is on the page, and at worst the test sits silently until it times out.
Logging is needed to know what is going on.