when @parametrize finds a fixture_ref in its argvalues, the parameter is not anymore accessible through request.getfixturevalue

[TheCaffinatedDeveloper]

Hi again @smarie!

Trying to figure out how to maintain the return values from cases that use a fixture as their own fixture name.

Example

conftest.py

@pytest.fixture
def some_fixture():
       return 1

@pytest.fixture(scope='function', autouse=True)
def some_other_fixture(request):
       # ouput will contain test_some_test_important_value_other_important_value as the fixture name
       print('fixturenames: ' + str(request.node.fixturenames))
       # hoping for important_value and other_important_value to be listed as fixtures

def case_some_case(some_fixture):
      important_value = some_fixture
      other_important_value = 2
      return important_value, other_important_value

mock_test.py

@parametrize_with_cases("important_value, other_important_value", cases='.')
def test_some_test(important_value, other_important_value):
       # important_value and other_important_value are here no problem
       assert important_value == 1
       assert other_important_value == 2

expected: [request, ..., ..., important_value, other_important_value, ...]
actual: [request, ..., ..., test_some_test_important_value_other_important_value, ...]

Note: this only happens when I use a fixture on the case.

[TheCaffinatedDeveloper]

I should note that I was able to use the follow to accomplish what I was looking for:

@fixture_plus
@parametrize_with_cases("important_value,other_important_value", cases='.')
def prepare_test_cases(important_value, other_important_value):
    return important_value, other_important_value

important_value, other_important_value = unpack_fixture("important_value,other_important_value", prepare_test_cases)

I didn't change anything in the case_ functions. While this works, it would be cool to have similar functionality for @parametrize_with_cases by having an option to prevent packing or union etc.

[smarie]

Hi @TheCaffinatedDeveloper , I am not sure to understand what the actual issue is.
All fixture names are preserved. However additional new fixtures are created automatically behind the scenes by @parametrize when there is at least a fixture_ref in the parameters. This happens when @parametrize_with_cases finds a case that relies on a fixture: it creates a fixture for the case, and then creates a fixture_ref pointing to it in the generated @parametrize.

So that is why you have for example test_some_test_important_value_other_important_value in the list.

If you compare the lists you should see that no name disappeared, only new names appeared. Let me know if this is not the case.

[TheCaffinatedDeveloper]

Hi @TheCaffinatedDeveloper , I am not sure to understand what the actual issue is.
All fixture names are preserved. However additional new fixtures are created automatically behind the scenes by @parametrize when there is at least a fixture_ref in the parameters. This happens when @parametrize_with_cases finds a case that relies on a fixture: it creates a fixture for the case, and then creates a fixture_ref pointing to it in the generated @parametrize.

So that is why you have for example test_some_test_important_value_other_important_value in the list.

If you compare the lists you should see that no name disappeared, only new names appeared. Let me know if this is not the case.

@smarie Thank you for your reply. That definitely makes sense. To clarify my example, if you print a list of fixtures using request.node.fixturenames the names do appear to be preserved here.

Even further, if you were use request.getfixturevalue('important_value') it would say that the fixture does not exist.

Again, this is only when a case_ is using a fixture_ref.

[TheCaffinatedDeveloper]

@smarie I know you are busy so I created a repl to demonstrate the issue:
Example

[smarie]

Thanks @TheCaffinatedDeveloper for this example ! I did not know about repl.it, quite cool :)

I copy the examples here for reproducibility

from pytest_cases import parametrize_with_cases

def case_without_fixture():
  important_value = 1
  other_important_value = 2
  return important_value, other_important_value 


@parametrize_with_cases("important_value,other_important_value", cases='.')
def test_case_without_fixture(request, important_value, other_important_value):
  # important_value and other_important_value are here no problem
  value = request.getfixturevalue('important_value').get()
  
  assert value == 1
  assert other_important_value == 2

and

from pytest_cases import parametrize_with_cases

def case_with_fixture(some_fixture):
  important_value = some_fixture
  other_important_value = 2
  return important_value, other_important_value

@parametrize_with_cases("important_value,other_important_value", cases='.')
def test_case_with_fixture(request, important_value, other_important_value):
  value = None
  try:
    value = request.getfixturevalue('important_value').get()
  except:
    print('Fixture not found :(')
  
  assert value == important_value
  assert important_value == 1
  assert other_important_value == 2

I think that there is a small misunderstanding here: important_value is not a fixture, this is a parameter. But since the pytest api is misleadingly named getfixturevalue it is quite normal to do the mistake :)
Ok I see the issue, and I'm afraid that this might be extremely difficult to fix. That being said, I'll have a look when I'm back to normal activity. Thanks !

[TheCaffinatedDeveloper]

@smarie Thanks, glad you found REPL.it useful 👍

[smarie]

Trying to reformulate this ticket in order to leave it open: when @parametrize finds a fixture_ref in its argvalues, the parameter is not anymore accessible through request.getfixturevalue.

Minimal example:

from pytest_cases import parametrize, fixture, fixture_ref

@parametrize("a", [1])
def test_without_fixture_ref(request, a):
    print(request._fixture_defs)
    assert request.getfixturevalue('a') == 1

@fixture
def some_fixture():
    return 1

@parametrize("a", [fixture_ref(some_fixture)])
def test_with_fixture_ref(request, a):
    print(request._fixture_defs)
    assert request.getfixturevalue('a') == 1

This is due to the fact that a does not exist as a parameter in the second case. Indeed @parametrize replaces test_with_fixture_ref with a wrapper function, depending on a newly generated fixture named test_with_fixture_ref_a. We can look at the console prints above to see it in request._fixture_defs.

So the second test is equivalent to

@fixture
def some_fixture():
    return 1

@fixture
def test_with_fixture_ref_a(some_fixture):
    return some_fixture

def test_with_fixture_ref(request, test_with_fixture_ref_a):
    a = test_with_fixture_ref_a
    print(request._fixture_defs)
    assert request.getfixturevalue('a') == 1

I'm afraid there is no simple solution to this problem... I suggest to close as "won't fix" except if you feel that this should be tackled. In that case we'll leave it open for community support