Q:

Easier way to test an existing DNN module?

Each time I want to test the DotNetNuke module I'm working on, I uninstall it from the DNN website host control panel, I zip my module dev folder, and then I reinstall it from the DNN website.
Is there any faster way to test my module?

A:

Are you testing the install process? 
If not - all the changes in DesktopModules/YourModule or App_Code/YourModule will take effect immediately and will be ready for testing (assuming you're using a Website project, and your virtual directory is pointing to your dev. directory)
If you're using the Web Application project - make changes, build, move the files to the virtual directory target folder, then test.
Let me know if this helps.

