Can you point me to a unit test that validates for example parsing of incoming commands to opensmtpd or ftpd or ntpd? Nothing. It is just not a common practice

Can you point me to a unit test that validates for example parsing of incoming commands to opensmtpd or ftpd or ntpd? Nothing. It is just not a common practice it seems. Now I don't think unit tests are a silver bullet. But having just code and zero tests is definitely a huge red flag for me.