`files(e)` logic seems to be incorrect for testing

[kevinansfield]

The files(e) conditional appears to be in the wrong order for testing because e.target.files will be an empty FileList which is truthy so the testingFiles branches are never reached.

I changed the behaviour in an override component to the following which is working fine for me but I may have missed something:

files(e) {
    return (e.originalEvent || e).testingFiles || e.target.files;
}

[cowboyd]

If you've gotten it working, where it wasn't working before, will be happy to integrate it into the upstream codebase!

I'm not seeing a test-case for the test helper.... bummer.