Craft more explicit tests covering tools.reader exception handling

[vemv]

Closes https://github.com/jonase/eastwood/issues/203

Expands test coverage in this area so we can be rest assured that this issue is in fact solved (which was for a long time, I'd say).

• [ ] You've updated the changelog (if adding/changing user-visible functionality)
• [ ] You've updated the readme (if eg adding a new linter)