[t-writescode]

If your software takes customer data, it is your responsibility to do what you can to protect that data; and tests are one of many necessary steps to protect customer data - you make sure that invalid input doesn’t give someone else’s secret data. Automated tests as part of merges are a great step in that certainty.

[massive-fail]

Yeah just don't be stupid, no need to test for stupid.

[geon]

Stupid is specifically what you need to test for.