> but my point is - you cannot do meaningful unit tests on very complex systems. I think you're missing the point: unit tests should not be testing entire syst

> but my point is - you cannot do meaningful unit tests on very complex systems. I think you're missing the point: unit tests should not be testing entire systems; that's the point of integration or end-to-end tests, which are different beasts entirely. You can very much write unit tests against parts of a complex system because each test should only be testing one isolated bit of functionality in the form of inputs (including local state) and outputs.