Test coverage for permission errors

[ericcornelissen]

Test Improvements

Summary

The integration tests currently do not cover the scenario where the user does not have the required permissions to remove a file or directory (except for what's mentioned in #1, which isn't intentional). This is the most important gap in the integration coverage for the code base at 155b391. Ideally this would be covered and ideally for both normal usage and --trash usage.