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pythoncachingpytest
Dimebag
Dimebag

Reputation: 843

Re-using data structure in pytest

I am working on a fairly versatile Python data structure while writing tests for every bit of functionality. Most of the tests re-instantiate the same structure, i.e. with the same values, such that a specific method can be tested. For example:

class T():
    def __init__(self, data):
        self.data = data

    def min(self):
        return 'min'

    def max(self):
        return 'max'

class TestT():
    def test_min():
        t = T(values)

        assert t.min() == 'min'

    def test_max():
        t = T(values)

        assert t.max() == 'max'

What is the proper way of re-using this t instance? I am only beginning and the tests are starting to take too long to execute. I want to speed them up.

Note: I am aware I could parametrize and getattr in this particular example but it would still instantiate t twice, once for each test.

Attempts

I looked at pytest.fixtures however it seems that making a fixture return this t would just do the same thing, re-instantiating it.

Pytest cache seems to be made for this but I do not understand from the documentation how to use it (what is request in the example?).

Lastly, just storing t in a (class) variable doesn't seem to speed up the tests.

Upvotes: 2

Views: 294

Answers (1)

Dimebag
Dimebag

Reputation: 843

It seems that my understanding of pytest fixtures was incomplete. The following works just fine:

class Test():
    @pytest.fixture(scope='class')
    def data(self):
        return ...

    def test_min(data):
        assert data.min() == 'min'

    def test_max(data):
        assert data.max() == 'max'

Upvotes: 1

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