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/world.dm

@@ -64,7 +64,12 @@ var/global/datum/global_init/init = new ()
 
 	. = ..()
 
+#if UNIT_TEST
+	log_unit_test("Unit Tests Enabled.  This will destroy the world when testing is complete.")
+	log_unit_test("If you did not intend to enable this please check code/__defines/unit_testing.dm")
+#else
 	sleep_offline = 1
+#endif
 
 	// Set up roundstart seed list.
 	plant_controller = new()
@@ -105,6 +110,9 @@ var/global/datum/global_init/init = new ()
 		processScheduler.deferSetupFor(/datum/controller/process/ticker)
 		processScheduler.setup()
 		master_controller.setup()
+#if UNIT_TEST
+		initialize_unit_tests()
+#endif
 
 	spawn(3000)		//so we aren't adding to the round-start lag
 		if(config.ToRban)