Parametrizing tests depending of also parametrized values in pytest

Question

I have a test where I have a setup method, that should receive a dataset, and a test function, that should run for each data in dataset

Basically I would need something like:

datasetA = [data1_a, data2_a, data3_a]
datasetB = [data1_b, data2_b, data3_b]

@pytest.fixture(autouse=True, scope="module", params=[datasetA, datasetB])
def setup(dataset):
    #do setup
    yield
    #finalize

#dataset should be the same instantiated for the setup
@pytest.mark.parametrize('data', [data for data in dataset]) 
def test_data(data):
    #do test

It should run like:

• setup(datasetA)
• test(data1_a)
• test(data2_a)
• test(data3_a)
• setup(datasetB)
• test(data1_b)
• test(data2_b)
• test(data3_b)

However it does not seem to be possible to parametrize over a variable obtained by a fixture, as I wanted to in the example.

I could have my function use a fixture and iterate inside the test method:

def test_data(dataset):
    for data in dataset:
        #do test

But then I would have one large test instead of a separate test for each case, which I would not like to have.

Is there any way of accomplishing this?

Thanks!

Answer 1

Answer #1: If strictly following you test design, then it should look like this:

import pytest

datasetA = [10, 20, 30]
datasetB = [100, 200, 300]

@pytest.fixture
def dataset(request):
    #do setup
    items = request.param
    yield items
    #finalize

@pytest.fixture
def item(request, dataset):
    index = request.param
    yield dataset[index]

#dataset should be the same instantiated for the setup
@pytest.mark.parametrize('dataset', [datasetA, datasetB], indirect=True)
@pytest.mark.parametrize('item', [0, 1, 2], indirect=True)
def test_data(dataset, item):
    print(item)
    #do test

Note the indirect parametrization for both item & dataset. The parameter values will be passed to the same-named fixture as request.param. In this case, we use the index in the assumption that the datasets are of the same length of 3 items.

Here is how it executes:

$ pytest -s -v -ra test_me.py 
test_me.py::test_data[0-dataset0] 10
PASSED
test_me.py::test_data[0-dataset1] 100
PASSED
test_me.py::test_data[1-dataset0] 20
PASSED
test_me.py::test_data[1-dataset1] 200
PASSED
test_me.py::test_data[2-dataset0] 30
PASSED
test_me.py::test_data[2-dataset1] 300
PASSED