Mock FS operations in integration tests?

Some tests specifically test things like FS operations: whether the report is correctly created, resources copied over, etc. Using some kind of mocked/virtual FS for these would improve isolation and give us more flexibility (e.g. possibly to test resilience to IO errors, etc).

I quickly tried a few options (with Jest’s built-in mocking features, or with `mock-fs`) but with no luck so far. To be further investigated.