How to replace test functions in py.test while collecting tests?

Question

I have a module with test functions and I want to write conftest.py file to decorate all functions in the module after the collection phase and before test run. And I do not want to edit the module with test functions. I tried it this way:

test_foo.py

def test_foo ():
    assert 1 == 42

conftest.py

def pytest_generate_tests (metafunc):
    def test_bar ():
        assert 1 == 2
    metafunc.function = test_bar

When I run tests, I get this:

==================================== FAILURES =====================================
____________________________________ test_foo _____________________________________

    def test_foo ():
>       assert 1 == 42
E       assert 1 == 42

But I expected assertion error about 1 == 2 .

Answer 1

If you want to run a certain function before a test , define a fixture and use the fixture name as test parameter.

import pytest


@pytest.fixture
def fixture1():
    assert 1 == 2


def test_foo(fixture1):
    assert 1 == 42

Output:

    @pytest.fixture
    def fixture1():
>       assert 1 == 2
E       assert 1 == 2

If you want to run a certain function before each test , define a fixture with autouse=True . I think this is what you want.

import pytest


@pytest.fixture(autouse=True)
def fixture1():
    assert 1 == 2


def test_foo():
    assert 1 == 42

Output:

    @pytest.fixture(autouse=True)
    def fixture1():
>       assert 1 == 2
E       assert 1 == 2

If you want a custom test decorator , use standard decorator syntax.

def my_test_decorator(test):
    def wrapper():
        assert 1 == 2

    return wrapper


@my_test_decorator
def test_foo():
    assert 1 == 42

Output:

    def wrapper():
>       assert 1 == 2
E       assert 1 == 2

Answer 2

我只需要替换pytest项目的runtest方法。