Activate and deactivate development mode.Source:
dev_mode creates a new library for storing installed
packages. This new library is automatically created when
activated if it does not already exist.
This allows you to test development packages in a sandbox, without
interfering with the other packages you have installed.
dev_mode(on = NULL, path = getOption("devtools.path"))
turn dev mode on (
TRUE) or off (
FALSE). If omitted will guess based on whether or not
directory to library.