Update sort_spec.lua

Author: icemberg

.spec/sorting/sort_spec.lua

@@ -75,3 +75,10 @@ end)
 describe("Bogosort", function()
 	check_sort(require("sorting.bogosort"), 5)
 end)
+describe("Countingsort", function()
+	-- Test with multiple radii
+	local countingsort = require("sorting.countingsort")
+	check_sort(countingsort(), nil, true)
+	check_sort(countingsort(2), nil, true)
+	check_sort(countingsort(1e3), nil, true)
+end)