[cowardlydragon]

mocking / interaction / expect breaks encapsulation to perform "testing".

Thus it is often a test of the implementation's assumptions when first written, and even worse, when the code is maintained/edited, the test is merely changed to get it to pass, because unit tests with mocks are usually:

1) fragile to implementation 2) opaque as to intent

Whereas input/output integration points are more reliable, transparent, and less fragile to implementation changes if the interface is maintained.

However, if you must do mock-level interaction testing, Spock has made it almost palatable in Javaland.

This is one area where functional fans get to make the imperative folks eat their lunch.

[YZF]

Exactly. I've seen tests where some code calls:

  printf("hello world");

And the test is:

  mock_printf(string) {
    if string != "hello world" then fail;
  }

Which is basically just duplicating your code as tests.