The `failed` function takes a mandatory first argument for the check name and a secondary optional argument for the message to display in verbose mode. Example :
```shell
test -f /path/to/file || failed "IS_FILE_EXISTS" "Missing file \`/path/to/file'"
```
If the test is in a loop and might yield multiple errors, It's better to print a single error in normal mode and every error in verbose mode.
```shell
for user in $users; do
if ! groups "$user" | grep -q adm; then
failed "IS_USERINADMGROUP" "User $user doesn't belong to \`adm' group"
test "${VERBOSE}" = 1 || break
fi
done
```
In a single check with multiple conditions, the verbose message helps determine which condition failed. Example :
```shell
if [ "$last_upgrade" -eq 0 ]; then
[ "$install_date" -lt "$limit" ] && failed "IS_NOTUPGRADED" "The system has never been updated"
else
[ "$last_upgrade" -lt "$limit" ] && failed "IS_NOTUPGRADED" "The system hasn't been updated for too long"
fi
```
### Use existing predicates
There are a few predicate functions that help making conditionals.
For Debian versions : `is_debian`, `is_debian_stretch`, `is_debian_jessie`…
For packs : `is_pack_web`, `is_pack_samba`.
For installed packages : `is_installed <package> [<package>]`.