Ok here are the Snapshots of everything I could get. Also I may have found the problem, but I doubt it. (Shown in snapshots)
Looks like you have everything in the right place for add-on development
Try this:
1 - start blockland
2 - start a custom game mode
3 - goto console and type:
exec("Add-ons/script_testing/server.cs");
4 - still in console, type:
test();
And your function should do its thing.
If you need to make changes in your .cs file, then re-run step 3 above (no need to restart blockland)
If you get errors (usually red text in the console) when running the exec() command, fix those, re-save the file and re-run the exec() command.