Screenshot Tests Airlocks (#91203)

## About The Pull Request

Tests that both normal and glass airlocks, and some of their overlays
work.

code/game/machinery/doors/airlock.dm

@@ -2533,6 +2533,7 @@
 	SEND_SIGNAL(src, COMSIG_AIRLOCK_OPEN, forced)
 	set_density(FALSE)
 	operating = FALSE
+	update_appearance()
 	return TRUE
 
 /obj/machinery/door/airlock/instant/close(forced = DEFAULT_DOOR_CHECKS, force_crush = FALSE)
@@ -2540,8 +2541,13 @@
 	SEND_SIGNAL(src, COMSIG_AIRLOCK_CLOSE, forced)
 	set_density(TRUE)
 	operating = FALSE
+	update_appearance()
 	return TRUE
 
+/obj/machinery/door/airlock/instant/glass
+	opacity = FALSE
+	glass = TRUE
+
 #undef AIRLOCK_SECURITY_NONE
 #undef AIRLOCK_SECURITY_IRON
 #undef AIRLOCK_SECURITY_PLASTEEL_I_S

code/modules/unit_tests/_unit_tests.dm

@@ -257,6 +257,7 @@
 #include "required_map_items.dm"
 #include "resist.dm"
 #include "say.dm"
+#include "screenshot_airlocks.dm"
 #include "screenshot_antag_icons.dm"
 #include "screenshot_basic.dm"
 #include "screenshot_digi.dm"

code/modules/unit_tests/screenshot_airlocks.dm

@@ -0,0 +1,40 @@
+/// Ensures common airlock overlays work
+/datum/unit_test/screenshot_airlocks
+
+/datum/unit_test/screenshot_airlocks/Run()
+	var/obj/machinery/door/airlock/instant/door = allocate(__IMPLIED_TYPE__)
+	var/obj/machinery/door/airlock/instant/glass/glass_door = allocate(__IMPLIED_TYPE__)
+
+	var/icon/final_icon = icon('icons/effects/effects.dmi', "nothing")
+
+	final_icon.Insert(getFlatIcon(door, no_anim = TRUE), dir = NORTH, frame = 1)
+	final_icon.Insert(getFlatIcon(glass_door, no_anim = TRUE), dir = SOUTH, frame = 1)
+
+	door.open()
+	glass_door.open()
+
+	final_icon = icon(final_icon)
+	final_icon.Insert(getFlatIcon(door, no_anim = TRUE), dir = NORTH, frame = 2)
+	final_icon.Insert(getFlatIcon(glass_door, no_anim = TRUE), dir = SOUTH, frame = 2)
+
+	door.close()
+	glass_door.close()
+	door.bolt()
+	glass_door.bolt()
+
+	final_icon = icon(final_icon)
+	final_icon.Insert(getFlatIcon(door, no_anim = TRUE), dir = NORTH, frame = 3)
+	final_icon.Insert(getFlatIcon(glass_door, no_anim = TRUE), dir = SOUTH, frame = 3)
+
+	door.unbolt()
+	glass_door.unbolt()
+	door.welded = TRUE
+	door.update_appearance()
+	glass_door.welded = TRUE
+	glass_door.update_appearance()
+
+	final_icon = icon(final_icon)
+	final_icon.Insert(getFlatIcon(door, no_anim = TRUE), dir = NORTH, frame = 4)
+	final_icon.Insert(getFlatIcon(glass_door, no_anim = TRUE), dir = SOUTH, frame = 4)
+
+	test_screenshot("icons", final_icon)