Test model with imagefield

I am having issues with testing models that contain imagefield and even file fields in general.
At first, I just passed in some random string but now my models actually do some checks on the file size and more this requiring an actual file.

How do I do this testing as I am not guaranteed some image will be in my media files at all times.

I would love to have a solution that relied on temporary files. But still hope for best practices

Here are some alternatives on testing file fields.

Thank you very much. That did the trick.