Fabrication is setting a field on your `Image` model called `filename` to the string value provided ("fake_image.png").
To get the behavior you want, it may depend on what is handling your image attachments. If you were using carrierwave your model would look something like this:
```
class Project
mount_uploader :featured_image
end
```
That will create a field on your model called `featured_image` and allow you to set an actual file object on it. Let's say you have an image file for your test suite at `spec/support/fake_image.png`. Your fabricator would look like this:
```
Fabricator(:project) do
featured_image { File.open(File.join(Rails.root, 'spec', 'support', 'fake_image.png')) }
end
```
It's actually providing the the image file to the field, not just the name of the file.