Fixes footprint stacking (#58918)

* Fixes footprint stacking, replace_decal needed to return parent, and just, didn't. I'm not sure where the fuck
this came from, or even how to test for it, but here you are

* Adds a unit test to prevent regressions on this error in future

* Uses TEST_ASSERT_EQUAL instead of TEST_ASSERT

Thank you moth man

Co-authored-by: Mothblocks <35135081+Mothblocks@users.noreply.github.com>

* Updates a comment to more accurately describe my pain

* maybe fixes it?

Co-authored-by: Mothblocks <35135081+Mothblocks@users.noreply.github.com>

code/game/area/space_station_13_areas.dm

@@ -49,6 +49,7 @@ NOTE: there are two lists of areas in the end of this file: centcom and station
 
 /area/testroom
 	requires_power = FALSE
+	has_gravity = STANDARD_GRAVITY
 	name = "Test Room"
 	icon_state = "storage"
 

code/game/objects/effects/decals/cleanable/humans.dm

@@ -288,8 +288,8 @@
 
 /obj/effect/decal/cleanable/blood/footprints/replace_decal(obj/effect/decal/cleanable/C)
 	if(blood_state != C.blood_state) //We only replace footprints of the same type as us
-		return
-	..()
+		return FALSE
+	return ..()
 
 /obj/effect/decal/cleanable/blood/footprints/can_bloodcrawl_in()
 	if((blood_state != BLOOD_STATE_OIL) && (blood_state != BLOOD_STATE_NOT_BLOODY))

code/modules/unit_tests/_unit_tests.dm

@@ -43,6 +43,7 @@
 #include "anchored_mobs.dm"
 #include "bespoke_id.dm"
 #include "binary_insert.dm"
+#include "bloody_footprints.dm"
 #include "breath.dm"
 #include "card_mismatch.dm"
 #include "chain_pull_through_space.dm"

code/modules/unit_tests/bloody_footprints.dm

@@ -0,0 +1,61 @@
+///Tests to make sure bloody footprits work as expected
+///So no stacking, they actually apply, and shoe staining thrown in for free
+/datum/unit_test/bloody_footprints
+
+/datum/unit_test/bloody_footprints/Run()
+	var/mob/living/carbon/human/blood_master = allocate(/mob/living/carbon/human)
+	var/obj/item/clothing/shoes/holds_blood = allocate(/obj/item/clothing/shoes)
+
+	blood_master.equip_to_slot_if_possible(holds_blood, ITEM_SLOT_FEET)
+
+	var/turf/open/move_to = get_step(blood_master, get_dir(blood_master, run_loc_floor_top_right))
+	//We need to not be "on" the same tile as the pool
+	blood_master.forceMove(move_to)
+
+	var/obj/effect/decal/cleanable/blood/pool = allocate(/obj/effect/decal/cleanable/blood)
+
+	//Max out the pools blood, so each step will make things stained enough to matter
+	pool.bloodiness = BLOOD_POOL_MAX
+
+	pool.forceMove(run_loc_floor_bottom_left)
+	blood_master.forceMove(run_loc_floor_bottom_left)
+
+	var/datum/component/bloodysoles/soles = holds_blood.GetComponent(/datum/component/bloodysoles)
+	var/blood_type = pool.blood_state
+
+	TEST_ASSERT(soles.bloody_shoes[blood_type], "Shoes didn't become stained after stepping in a pool of [blood_type]")
+
+	//The bloody soles component handles the order of stepping on blood/stepping on a bloody tile in a constranating way
+	//Which means it needs to check and see if any time has passed between steps, so it can be sure the player is stepping onto a new tile (that should become bloody)
+	//I on the other hand need to do all my movements in one tick, so we need to sidestep this check
+	//Please kill me slowly
+	soles.last_pickup -= 1
+
+	//Move off the bloody tile, time to do some testing
+	blood_master.forceMove(move_to)
+
+	soles.last_pickup -= 1
+	blood_master.forceMove(run_loc_floor_bottom_left)
+
+	var/footprint_total = 0
+	for(var/obj/effect/decal/cleanable/blood/footprints/print_set in move_to)
+		if(print_set.blood_state == blood_type)
+			footprint_total += 1
+
+	TEST_ASSERT(footprint_total, "The floor didn't get covered in [blood_type] after being walked over")
+
+	soles.last_pickup -= 1
+
+	//Another set of movements to try and make some doubled up prints
+	blood_master.forceMove(move_to)
+
+	soles.last_pickup -= 1
+	blood_master.forceMove(run_loc_floor_bottom_left)
+
+	footprint_total = 0
+	for(var/obj/effect/decal/cleanable/blood/footprints/print_set in move_to)
+		if(print_set.blood_state == blood_type)
+			footprint_total += 1
+
+	TEST_ASSERT(footprint_total, "The floor somehow lost its footprints after being walked over")
+	TEST_ASSERT_EQUAL(footprint_total, 1, "The floor had more than one set of footprints in it, something is fucked")

code/modules/unit_tests/unit_test.dm

@@ -50,7 +50,7 @@ GLOBAL_VAR(test_log)
 	// clear the test area
 	for (var/turf/turf in block(locate(1, 1, run_loc_floor_bottom_left.z), locate(world.maxx, world.maxy, run_loc_floor_bottom_left.z)))
 		for (var/content in turf.contents)
-			if (iseffect(content))
+			if (istype(content, /obj/effect/landmark))
 				continue
 			qdel(content)
 	return ..()