> mock the filesystem it's beautiful in theory. but reality goes like this: "i only have this little method. writing mocks will take 5x more time then the code

> mock the filesystem it's beautiful in theory. but reality goes like this: "i only have this little method. writing mocks will take 5x more time then the code. i will just test the side effects on the functional tests" then, a year later, the team added a dozen methods that would benefit from the mock, but since you did the first one in functional only, the team just added the new ones there as well. the end. (because nobody refactor projects for tests) :(