When loading a gig file, all rackspaces are loaded one after the others and the different scripts are also started. Each time a script is started, the Initialization section is executed, then every widget callbacks are called for initialization and finally the On Activate callback is called too. This means that in a normal use situation, a script never runs without having the widgets and On Activate callbacks called at least once.
However, it seems there is an exception, which is when compiling. Indeed, after a compilation, only the Initialization section is started, and the script runs in a configuration that never happens in a normal use situation. So, to test a script in a context reflecting a normal use situation, it is necessary to add an additionnal rackspace, to switch to it and to switch back to the rackspace containing the script. Then the different callbacks are called and the test can be achieved properly.
It could perhaps be nice to start the different callbacks after compiling to put the script in a standard running configuration?