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/unit_tests/mob_tests.dm

@@ -0,0 +1,29 @@
+/datum/unit_test/space_suffocation
+	name = "MOB: human mob suffocates in space"
+
+	var/startOxyloss
+	var/endOxyloss
+	var/mob/living/carbon/human/H
+	async = 1
+
+/datum/unit_test/space_suffocation/start_test()
+	var/turf/space/T = locate()
+
+	H = new(T)
+	startOxyloss = H.getOxyLoss()
+
+	return 1
+
+/datum/unit_test/space_suffocation/check_result()
+	if(H.life_tick < 10)
+		return 0
+
+	endOxyloss = H.getOxyLoss()
+
+	if(startOxyloss < endOxyloss)
+		pass("Human mob takes oxygen damage in space. (Before: [startOxyloss]; after: [endOxyloss])")
+	else
+		fail("Human mob is not taking oxygen damage in space. (Before: [startOxyloss]; after: [endOxyloss])")
+
+	qdel(H)
+	return 1