Auto merge of #10706 - merelymyself:master, r=epage

Auto merge of #10706 - merelymyself:master, r=epage

Guide new users to add use `super::*;` to `mod test`

### What does this PR try to resolve?

Currently, `cargo init --lib` produces examples for unit tests. However, new users will find that they are unable to use functions they defined above. This should resolve the confusion.

Fixes #10559

### How should we test and review this PR?

This PR does not create new features. Test this PR using the already-existing tests.

### Additional information

I didn't think this was a major change, so I did not open a RFC for it. Please let me know if I should have!