It really slows down your test suite accessing the disk.So yes, in principle it slows down your tests. There is a "school of testing" where developer should isolate the layer responsible for retrieving state and just set some state in memory and test functionality (as if Repository pattern). The thing is Rails is a tightly coupled with implementation logic of state retrieval on core level and prefers "school of testing" in which you couple logic with state retrial to some degree.Good example of this is how models are tested in Rails. You could just build entire test suite calling `FactoryBot.build` and never ever use `FactoryBot.create` and stub method all around and your tests will be lighting fast (like 5s to run your entire test suite). This is highly unproductive to achieve and I failed many times trying to achieve that because I was spending more time maintaining my tests then writing something productive for business.Or you can took more pragmatic route and save database record where is too difficult to just 'build' the factory (e.g. Controller tests, association tests etc)Same I would say for saving the file to the Disk. Yes you are right You could just "not save the file to disk" and save few milliseconds. But at the same time you will in future stumble upon scenarios where your tests are not passing because the file is not there (e.g. file processing validations) Is it really worth it ? I never worked on a project where saving file to a disk would slow down tests significantly enough that would be an issue (and I work for company where core business is related to file uploading) Especially now that we have SSD drives in every laptop/server it's blazing fast so at best you would save 1 seconds for entire test suite (given you call FactoryBot traits to set/store file where it make sense. Not when every time you build an object.)

Working is better than perfect.

It is about balancing the twin needs of writing good software, and writing any software at all.