In some languages A might free a memory allocation e.g. after communicating with some server. If B also frees that memory then there is a bug. Presumably this

In some languages A might free a memory allocation e.g. after communicating with some server. If B also frees that memory then there is a bug. Presumably this means B's tests are wrong/incomplete. If B was mocking A to avoid the IO, you might not find out.