The post is not about what you're sending, it is about making sure what you're receiving is what you're getting. The motivation begins with: "Many of our programs accept input from the user. Often we need to validate this input before continuing processing and, in the case of errors, inform the user of any problems."

You may also want to do sanity checks but, in those cases, I tend to deliberately abuse the inputs. Send a string, a byte string, some invalid UTF-8, an emoji, an invoice, and ensure that the thing can take more abuse than what the manual says.

If, however, the manual says “integer” then it should complain loudly the user is breaking the contract.