Fix buckling and probably a lot more mousedrop interactions (#93352)

code/modules/unit_tests/_unit_tests.dm

@@ -110,6 +110,7 @@
 #include "blindness.dm"
 #include "bloody_footprints.dm"
 #include "breath.dm"
+#include "buckle.dm"
 #include "burning.dm"
 #include "cable_powernets.dm"
 #include "can_see.dm"

code/modules/unit_tests/buckle.dm

@@ -0,0 +1,36 @@
+/// Test you can buckle yourself to a chair
+/datum/unit_test/buckling_self
+
+/datum/unit_test/buckling_self/Run()
+	var/mob/living/carbon/human/consistent/dummy = EASY_ALLOCATE()
+	dummy.mock_client = new()
+	var/obj/structure/chair/chair = EASY_ALLOCATE()
+
+	var/old_usr = usr
+
+	usr = dummy // mouse drop still uses usr
+
+	dummy.MouseDrop(chair)
+	if(dummy.buckled != chair)
+		TEST_FAIL("The dummy failed to buckle themselves to a chair via mouse drop.")
+
+	usr = old_usr
+
+/// Test you can buckle someone else to a chair
+/datum/unit_test/buckling_others
+
+/datum/unit_test/buckling_others/Run()
+	var/mob/living/carbon/human/consistent/dummy = EASY_ALLOCATE()
+	dummy.mock_client = new()
+	var/mob/living/carbon/human/consistent/victim = EASY_ALLOCATE()
+	var/obj/structure/chair/chair = EASY_ALLOCATE()
+
+	var/old_usr = usr
+
+	usr = dummy // mouse drop still uses usr
+
+	victim.MouseDrop(chair)
+	if(victim.buckled != chair)
+		TEST_FAIL("The dummy failed to buckle the victim to a chair via mouse drop.")
+
+	usr = old_usr