Testing class methods with pytest

Question

In the documentation of pytest various examples for test cases are listed. Most of them show the test of functions. But I’m missing an example of how to test classes and class methods. Let’s say we have the following class in the module cool.py we like to test:

class SuperCool(object):

    def action(self, x):
        return x * x

How does the according test class in tests/test_cool.py have to look?

class TestSuperCool():

    def test_action(self, x):
        pass

How can test_action() be used to test action()?

Asked By: laserbrain

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Source

Answer 1

All you need to do to test a class method is instantiate that class, and call the method on that instance:

def test_action(self):
    sc = SuperCool()
    assert sc.action(1) == 1

Answered By: elethan

Answer 2

Well, one way is to just create your object within the test method and interact with it from there:

def test_action(self, x):
    o = SuperCool()
    assert o.action(2) == 4

You can apparently use something like the classic setup and teardown style unittest using the methods here: http://doc.pytest.org/en/latest/xunit_setup.html

I’m not 100% sure on how they are used because the documentation for pytest is terrible.

Edit: yeah so apparently if you do something like

class TestSuperCool():
    def setup(self):
        self.sc = SuperCool()

    ... 

    # test using self.sc down here

Answered By: Tyler Sebastian

Answer 3

I would use any fixtures only to create test environment (like database connection) or data parametrization.

If your data is relatively trivial, you can define it inside the testcase:

def test_action_without_fixtures():
    sc = SuperCool()
    sc.element = 'snow'
    sc.melt()
    assert sc.element == 'water'

Example with parametrization:

@pytest.mark.parametrize("element, expected", [('snow', 'water'), ('tin', 'solder')])
def test_action_with_parametrization(element, expected):
    sc = SuperCool()
    sc.element = element
    sc.melt()
    assert sc.element == expected

Answered By: klapshin

Testing class methods with pytest

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