In #9726 I refactored the infrastructure of the core package, but one option I was not immediately able to translate to the new infrastructure was the --readonly option to test. See #9726 (comment) for more details. This issue is a reminder that we should find a way to ensure that no files are written outside of temporary directories during tests. I'm assigning myself, but if anyone wants to tackle this please let me know as any help would be appreciated!