Hi Holger,
On 19 sep 2014, at 09:52, holger krekel <[email protected]> wrote:
> I presume that with module and class scope people don't presume that
> a fixture survives until the end of a process so eager teardown is less
> of a problem, there, right?
I have not fully grasped how fixture teardown currently happens in pytest. To
explore it, I came up with this example:
import pytest
@pytest.yield_fixture(scope='class')
def fix():
print 'fixture setup'
yield
print 'fixture teardown'
class TestFoo():
def test_a(self, fix):
print 'test_a'
def test_b(self):
print 'test_b'
def test_c(self, fix):
print 'test_c'
It gives me the output (with the latest pytest from PyPI):
fixture setup
test_a
test_b
test_c
fixture teardown
I.e. even though test_b does not actively request the fixture, it is active
during the test.
Is this even considered to be a bug or a feature? :-) This behavior may be
considered a bug since it makes test suites brittle - if the fixture does not
contain a value itself, it can probably be neglected to actually properly
request the fixture, but test_b will still accidentally have “fix” available.
Bugs like this will only show itself when running a subset of the test suite
(and with xdist!).
I would prefer (I think) if all fixtures where torn down when they are not
requested (in my example, before test_b is run, to ensure test_b is only run
with its own fixtures).
However, if all teardowns worked like this, the efficiency will be very bad
since there will be a lot of teardowns. I think these fixtures that should be
allowed to stay alive, should be explicitly declared like that, like the option
to pytest.fixture() suggested earlier.
I think this makes sense regardless of whether the fixture is class, module or
session scoped. Having different semantics depending on the scope would be
confusing. Fixture authors must be aware and decide whether or not a fixture
may accidentally be available to wrong tests. I have a hard time to see how we
can solve this properly without a flag or some kind of distinction for this.
I am probably missing a lot of details here, what are your thoughts on this?
Cheers,
Andreas
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