Mech construction fix and unittest (#18849)

* these need to be vars apparently

* testing

* spawn construct

* macro fix

* as anything

* allow null...

* consistency

code/modules/unit_tests/_unit_tests.dm

@@ -91,6 +91,7 @@
 #include "autowiki.dm"
 //#include "clothing_tests.dm" // FIXME
 #include "component_tests.dm"
+#include "construction_tests.dm"
 #include "cosmetic_tests.dm"
 #include "dcs_check_list_arguments.dm"
 #include "dcs_get_id_from_elements.dm"

code/modules/unit_tests/construction_tests.dm

@@ -0,0 +1,11 @@
+/datum/unit_test/mech_construction/Run()
+	var/failed = FALSE
+	for(var/datum/construction/C as anything in subtypesof(/datum/construction))
+		// We check for null, as null is legal here... For now... Mech construction needs a full refactor to make them unittest-able in a not ugly way.
+		if(!C.result)
+			continue
+		if(!ispath(C.result))
+			TEST_NOTICE(src, "[C.type]: Mech Construction - Had invalid result \"[C.result]\", must be a path.")
+			failed = TRUE
+	if(failed)
+		TEST_FAIL("Mech Construction - A construction datum had incorrect data.")