[pjc50]

That's a good example, because while they're clearly different things, any distinction you draw between them such as "population > 100k" or "has cathedral" is always going to be a bit arbitrary, and many cities grew organically from villages in an unplanned manner.

[randomdata]

Is it? Kent Beck, coiner of unit test, made himself quite clear that a unit test is a test that is independent (i.e. doesn't cause other tests to fail). For all the ridiculous definitions I have come across, I have never once heard anyone call an integration test a test that is dependent (i.e. may cause other tests to fail). In reality, a unit test and an integration test are the same thing.

The post facto attempts at differentiation never make sense. For example, another comment here proposed that a unit test is that which is not dependent on externally mutable dependencies (e.g. the filesystem). But Beck has always been adamant that unit tests should use the "real thing" to the greatest extent possible, including using the filesystem if that's what your application does.

Now, if one test mutates the filesystem in a way that breaks another test, that would violate what Beck calls a unit test. This is probably the source of confusion in the above. Naturally, if you don't touch the file system there is no risk of conflicting with other tests also using the filesystem. But that really misses the point.