register tests only if enabled (#38)

Co-authored-by: BuckarooBanzay <BuckarooBanzay@users.noreply.github.com>

init.lua

@@ -44,7 +44,7 @@ end)
 
 dofile(modpath .. "/src/commands.lua")
 
-if minetest.get_modpath("mtt") then
+if minetest.get_modpath("mtt") and mtt.enabled then
     -- register tests
     dofile(modpath .. "/mtt.lua")
 end

mtt.lua

@@ -4,4 +4,7 @@ mtt.emerge_area({ x=0, y=0, z=0 }, { x=10, y=10, z=10 })
 
 -- check nodelist
 local mtt_nodelist = minetest.settings:get("mtt_nodelist")
+if mtt_nodelist then
+    -- nodelist specified, check if all the required nodes are present
     mtt.validate_nodenames(minetest.get_modpath("xcompat") .. "/test/nodelist/" .. mtt_nodelist)
+end