Write more tests

[BurnySc2]

Test the following scenarios:

• [ ] Have burrowed or invisible enemy units next to terran structure that want to build an addon - will there be an action_error?
• [ ] Have a tank from high ground or far distance (with vision helper) that should be displayed as "snapshot" - will it be a "snapshot" or will the visibility "visible"?
• [ ] Test if a bunker loaded with units is marked as .is_active, or only if it is shooting.