please dont break chain grabs

code/modules/grab/grab_living.dm

@@ -103,7 +103,7 @@
 
 	for(var/obj/item/hand_item/grab/G in active_grabs)
 		var/atom/movable/pulling = G.affecting
-		if(!MultiZAdjacent(src, pulling))
+		if(!MultiZAdjacent(pulling))
 			qdel(G)
 		else if(!isturf(loc))
 			qdel(G)

code/modules/unit_tests/mobswap.dm

@@ -0,0 +1,40 @@
+/datum/unit_test/mob_swap_grab
+	name = "BUMPSWAP: Swapping Shall Break Grabs Under Correct Conditions"
+
+/datum/unit_test/mob_swap_grab/Run()
+	var/mob/living/carbon/human/grabbed = ALLOCATE_BOTTOM_LEFT()
+	var/mob/living/carbon/human/grabber = ALLOCATE_BOTTOM_LEFT()
+	var/mob/living/carbon/human/bumped = ALLOCATE_BOTTOM_LEFT()
+
+	grabber.forceMove(get_step(grabber, EAST))
+	grabbed.forceMove(get_step(grabber, EAST))
+
+	grabber.try_make_grab(grabbed)
+
+	TEST_ASSERT(grabber.is_grabbing(grabbed), "Grabber failed to grab the target.")
+
+	step(grabber, WEST)
+
+	TEST_ASSERT(grabber.loc == run_loc_floor_bottom_left, "Grabber did not end up on the correct turf.")
+	TEST_ASSERT(!grabber.is_grabbing(grabbed, "Grab did not release after shuffling away."))
+
+/datum/unit_test/mob_swap_grab_inverse
+	name = "BUMPSWAP: Swapping Shall Not Break Grabs Under Correct Conditions"
+
+/datum/unit_test/mob_swap_grab_inverse/Run()
+	var/mob/living/carbon/human/grabbed = ALLOCATE_BOTTOM_LEFT()
+	var/mob/living/carbon/human/grabber = ALLOCATE_BOTTOM_LEFT()
+	var/mob/living/carbon/human/bumped = ALLOCATE_BOTTOM_LEFT()
+
+	grabber.forceMove(get_step(grabber, EAST))
+	grabbed.forceMove(get_step(grabber, NORTH))
+
+	grabber.try_make_grab(grabbed)
+
+	TEST_ASSERT(grabber.is_grabbing(grabbed), "Grabber failed to grab the target.")
+
+	step(grabber, WEST)
+
+	TEST_ASSERT(grabber.loc == run_loc_floor_bottom_left, "Grabber did not end up on the correct turf.")
+	TEST_ASSERT(grabber.is_grabbing(grabbed, "Grab released after shuffling, despite being adjacent still."))
+