Adds unit tests

Port of https://github.com/Baystation12/Baystation12/pull/11808 and
several others
Fixes three overlapping cables ([192 / 158 / 1], [214 / 161 / 1], [122 /
197 / 1])
Fixes drill and mech drill having the same ID.

code/_helpers/logging.dm

@@ -82,6 +82,9 @@
 /proc/log_misc(text)
 	diary << "\[[time_stamp()]]MISC: [text][log_end]"
 
+/proc/log_unit_test(text)
+	world.log << "## UNIT_TEST: [text]"
+
 //pretty print a direction bitflag, can be useful for debugging.
 /proc/print_dir(var/dir)
 	var/list/comps = list()