unit testing

Unit testing aka white box testing means you write a test that is aware of the implementation. It means that you can write fine grained tests specific to a set of requirements. Integration tests (or whatever you wanna call them) test multiple artifacts cooperating together. Theoretically a unit test tests the implementation of one method and nothing else. However this distinction is hard to make when the tests evolve.

Suppose you start with two different test folders: unit-test and integration-test. First couple of days everything is working nicely. One day you decide to refactor a piece of code. Luckily you are disciplined enough to move the tests along with the code to the new packages. However one of the methods that was white box tested had a piece that was extracted to a new method (let's say within the same class). Now suddenly this test you had written is no longer testing solely one method. Hmmm.

Thinking of this; if I write a unit test for a method and this method calls a couple of JVM routines, is it a unit test or an integration test from the beginning?

Point i'm trying to make is that if you want to be really strict about separating unit and integration tests it takes an enormous effort to keep it sound. With large teams - people come and go - in time it will be an impossible task.