Fixed failing tests due to the change we check for file readability.

[kberov]

No description provided.

[HeikoSchlittermann]

I added another commit with a serving suggesting :) I strongly believe, you should not try to parse error strings. Use sentinel errors instead. Or return the errors you got from the os, if possible.

And, if you do fmt.Errorf, use %w to Wrap and not convert the errors.

[kberov]

@HeikoSchlittermann, thanks for the suggestion. In tests now I use errors.Is(...) instead of parsing error strings.