Test case editor fails to load

Problem

Using the Edit action on a Test Case does not result in the Test Case editor loading. The editor fails to load, and displays an error message instead:

Solution

This has been known to be caused by a third party app incorrectly adding JavaScript resources to all Jira web pages:

  • Xray Test Management for Jira (version 3.3.8 and lower)

Upgrading the above app to a higher version (at least 3.4.0) should solve the problem.