+# Explicitly require external prerequisite. Useful when binary is
+# called indirectly (e.g. from emacs).
+# Returns success if dependency is available, failure otherwise.
+test_require_external_prereq () {
+ binary="$1"
+ if [ "$(eval echo -n \$test_missing_external_prereq_${binary}_)" = t ]; then
+ # dependency is missing, call the replacement function to note it
+ eval "$binary"
+ else
+ true
+ fi
+}
+