[Tutor] More on unit testing - tests for external data...

[Modulok]

List,

Unit testing functions and methods which rely on passed data is simple
enough. However:

How do I unit test something which relies on external data?

For example, a function which creates a file only if it doesn't exist
on disk, or a unit test for a function which makes an SQL query? If
anyone could point to a few examples of such usage, that would be
great!

Thanks!
-Modulok-