Separate packages for mocks?

Say I have a package which handles sending emails over SMTP. Many of the apps I build use it. For unit testing purposes, I create a mock of the email service from that package which logs raw mail content to a file instead of sending it over SMTP. It seems like the mock therefore belongs to the mail package, rather than to be repeated in every app. But the mock uses another package which handles logging. And a mail package should not depend on a logging package I think. How to resolve that? Should there be a separate "mail mock" package which uses both the mail and the logger packages? Note that ChatGPT unequivocally says "yes". But I am wondering how human being software architects would handle it. I've never heard of packages to exist solely for the purposes of mocking another package.

Apr 5, 2025 - 15:53

Say I have a package which handles sending emails over SMTP. Many of the apps I build use it.

For unit testing purposes, I create a mock of the email service from that package which logs raw mail content to a file instead of sending it over SMTP.

It seems like the mock therefore belongs to the mail package, rather than to be repeated in every app.

But the mock uses another package which handles logging. And a mail package should not depend on a logging package I think.

How to resolve that? Should there be a separate "mail mock" package which uses both the mail and the logger packages?

Note that ChatGPT unequivocally says "yes".

But I am wondering how human being software architects would handle it. I've never heard of packages to exist solely for the purposes of mocking another package.