The purpose of this request is to provide a way for a safe testing environment when developing new or improving upon current features that could possibly alter or disrupt the normal usage of Joplin.
In its current state, Joplin doesn’t have a safety net protecting user’s content when that user is working with the source code and this could be devastating if a feature is implemented incorrectly during their tests. Also, not everyone is thorough about backing up their content and configurations; I believe that a feature like this could help immensely with that (despite not taking precautions being the fault of the user).
The way that I would implement this feature:
Add a --dev-mode flag; this would tell Joplin that it is not being ran for normal usage.
Create a developer database separate from the main one to ensure a clean configuration and environment to remove the possibility of harming the user’s personal content
Replace the Welcome Notebook with a Developer Guidelines Notebook that gives practical information about testing new features before submitting them as a Pull Request and other useful information for contributors old and new. I think this should be permanent and cannot be deleted.