Dev: cannot write test for file uploading

[kenjis]

We currently don't have a great way to test file uploads for end users.

See https://forum.codeigniter.com/showthread.php?tid=88557

Reference: kenjis/ci-phpunit-test#157

[kenjis]

It would be nice to be able to simply provide a CodeIgniter\Files\UploadedFile object to the request and have it recognize it correctly, set the enctype header, and just work...
#8209

[damian-romanowski]

I could really use this feature. Currently I just test the error paths, but have to ignore coverage for anything under that that uses the actual upload.