fixup! infr: Add some testing infrastructure

check.sh

@@ -27,6 +27,7 @@ sorted=$($TOP/sort.sh /dev/stdout)
 # check whether input is sorted
 if [[ "${input}" != "${sorted}" ]]
 then
+    diff <(echo "${input}") <(echo "${sorted}")
     echo "Input not sorted! Consider running 'sort.sh'"
     exit 1
 fi