Problem
During a Test creation/edition, are you facing the error below?
Error Creating/Saving Step Request failed with status code 404
Solution
If this is the case, the solution is simple! 
Be sure that atlassian-addons-project-access is granted with the Browse, Create Issues, and Edit Issues permissions!
Nevertheless, if you have them set will kindly ask you to please remove atlassian-addons-project-access from these three permissions and add them again.