Fixes timer buckets going into negatives and adds a regression test

code/modules/unit_tests/_unit_tests.dm

@@ -1,9 +1,11 @@
 //include unit test files in this module in this ifdef
+//Keep this sorted alphabetically
 
 #ifdef UNIT_TESTS
-#include "unit_test.dm"
-#include "reagent_recipe_collisions.dm"
 #include "reagent_id_typos.dm"
+#include "reagent_recipe_collisions.dm"
 #include "spawn_humans.dm"
 #include "subsystem_init.dm"
+#include "timer_sanity.dm"
+#include "unit_test.dm"
 #endif

code/modules/unit_tests/timer_sanity.dm

@@ -0,0 +1,3 @@
+/datum/unit_test/timer_sanity/Run()
+	if(SStimer.bucket_count < 0)
+		Fail("SStimer is going into negative bucket count from something")