CODEWITHSUNDEEP
pythonunit-testingdecoratorpytest
jck
jck

Reputation: 2058

How do I make pytest fixtures work with decorated functions?

py.test seems to fail when I decorate test functions which has a fixture as an argument.

def deco(func):

    @functools.wraps(func)
    def wrapper(*args, **kwargs):
        return func(*args, **kwargs)

    return wrapper


@pytest.fixture
def x():
    return 0

@deco
def test_something(x):
    assert x == 0

In this simple example, I get the following error:

TypeError: test_something() takes exactly 1 argument (0 given).

Is there a way to fix this, preferably without modifying the decorator too much? (Since the decorator is used outside testing code too.)

Upvotes: 56

Views: 28943

Answers (3)

Jurgen Strydom
Jurgen Strydom

Reputation: 3930

In the case where you are using a pytest fixture with a decorator while passing data to the decorator, you can do it as follows:

import pytest

@pytest.fixture(scope="session")
def data(request):
    data = list(range(10))
    yield data

def decorator_with_variable_and_fixture(whatever):
    def wrap(test_func):
        def wrapper(data):
            mod = whatever.lower()[::-1]
            test_func(data, mod)
        return wrapper
    return wrap

@decorator_with_variable_and_fixture(whatever='SOMETHING!')
def test_decorator_with_variable_and_fixture(data, whatever):
    for i in data:
        print(whatever[i]*(i+1))
    assert whatever == '!gnihtemos'
    assert data == list(range(10))

Note how data is passed to the wrapper function - this way pytest's fixture approach still works correctly.

This is quite handy for example if you need to pass a PySpark session around, while using a decorator to perform other functionality.

Upvotes: 1

jck
jck

Reputation: 2058

It looks like functools.wraps does not do the job well enough, so it breaks py.test's introspection.

Creating the decorator using the decorator package seems to do the trick.

import decorator

def deco(func):
    def wrapper(func, *args, **kwargs):
        return func(*args, **kwargs)
    return decorator.decorator(wrapper, func)

Upvotes: 54

falsetru
falsetru

Reputation: 369394

Fixture feature depends on test function signature.

If you can change wrapper signature as follow, it will works.

def deco(func):
    @functools.wraps(func)
    def wrapper(x):
        return func(x)
    return wrapper

If you can't change it, make another decorator:

def deco(func):
    @functools.wraps(func)
    def wrapper(*args, **kwargs):
        return func(*args, **kwargs)
    return wrapper

def deco_x(func):
    @functools.wraps(func)
    def wrapper(x):
        return func(x)
    return wrapper

And decorate test_somthing with deco_x:

@deco_x
@deco
def test_something(x):
    assert x == 0

Upvotes: 10

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