Add support for using the same fixture twice in a function

[torfsen]

I often end up using the same fixture twice (or even more times) in the same function, for example to get two temporary directories using tmp_path. As far as a I know, this is currently only possible by manually creating a copy of the fixture:

tmp_path2 = tmp_path

def test_foo(tmp_path, tmp_path2):
    assert something

I would love to see native support for this, and I think keyword arguments would be a nice way to achieve this from the user's perspective:

def test_foo(input_path=tmp_path, output_path=tmp_path):
    assert something

This would give the user two (or more) independent instances of the fixture.

I don't know enough about the pytest internals to judge how hard this would be to implement, though.

[RonnyPfannschmidt]

its currently very far away, i strongly suggest to simply make 2 fixtures that each create a different folder within the test tmpdir for the time being

[asottile]

I don't think we could ever enable something like this, there's too many test suites depending on fixtures being the same instance across tests / fixtures.

Note also that the doubling of fixtures suggested on SO doesn't really work, they're exactly the same fixture:

import pytest

@pytest.fixture
def tmpdir2(tmpdir):
    yield tmpdir


def test(tmpdir, tmpdir2):
    assert tmpdir is tmpdir2

$ pytest t.py
============================= test session starts ==============================
platform linux -- Python 3.6.8, pytest-5.2.0, py-1.8.0, pluggy-0.13.0
rootdir: /tmp/x
collected 1 item                                                               

t.py .                                                                   [100%]

============================== 1 passed in 0.01s ===============================

The suggestion is to make a fixture or set of fixtures which represent your individual sub-directories:

@pytest.fixture
def input_dir(tmpdir):
    return tmpdir.join('input').ensure_dir()


@pytest.fixture
def output_dir(tmpdir):
    return tmpdir.join('output').ensure_dir()


def test(input_dir, output_dir):
    ...

[RonnyPfannschmidt]

@asottile i dont consider the concept itself unthinkable/bad - but it first needs a sound underpinning

its unattainable before the implementation of fixtures is refactored

[asottile]

well for one, keyword arguments wouldn't work -- where would the tmp_path default value come from (and that would be a break in and of itself for existing things using default values)? what would the scope of such fixtures be (it couldn't be function as then they'd be identical again)

I don't think this is worth complicating fixtures and I don't think the implementation would be easy (nor the complexity worth it) -- plus it would break all testsuites assuming shared fixtures which has been the behaviour since the beginning afaict

[RonnyPfannschmidt]

the required complexity will automatically come from multi-scope fixtures and invocation/usage scope fixtures

[asottile]

are there plans for that? I don't even know what that means

[RonnyPfannschmidt]

multi scope is being able to have fixtures availiable at different scopes using the same name
usage scope is having the fixture that depends on you determine/enforce the scope

invocation scope is having one fixture instance per request of a fixture

[Zac-HD]

Closing as duplicate of #2703, which has some more detail on the implementation challenges and interim workarounds (i.e. fixtures providing factories).