I have a couple of fixtures that do some initialization that is rather expensive. Some of those fixtures can take parameters, altering their behaviour slightly.
Because these are so expensive, I wanted to do initialisation of them once per test class. However, it does not destroy and reinit the fixtures on the next permutation of parameters.
See this example: https://gist.github.com/vhdirk/3d7bd632c8433eaaa481555a149168c2
I would expect that StuffStub would be a different instance when DBStub is recreated for parameters 'foo' and 'bar'.
Did I misunderstand something? Is this a bug?
This is not a bug. There is no relation between the fixtures so one of them is not going to get called again just because the other one was due to having multiple params.
In your case db is called twice because db_factory that it uses has 2 params. The stuff fixture on the other hand is called only once because stuff_factory has only one item in params.
You should get what you expect if stuff would include db_factory as well without actually using its output (db_factory would not be called more than twice):
@pytest.fixture(scope="class")
def stuff(stuff_factory, db_factory):
return stuff_factory()