pytest -> How to use fixture return value in test method under a class

问题

I have a fixture that returns a value like this:

import pytest

@pytest.yield_fixture(scope="module")
def oneTimeSetUp(browser):
    print("Running one time setUp")
    if browser == 'firefox':
        driver = webdriver.Firefox()
        print("Running tests on FF")
    else:
        driver = webdriver.Chrome()
        print("Running tests on chrome")
    yield driver
    print("Running one time tearDown")

This fixture gets the browser value from another fixture which is reading the command line option.

Then I have a test class where I have more than one test methods and they all want to consume the same returned value driver to proceed the tests.

import pytest

@pytest.mark.usefixtures("oneTimeSetUp")
class TestClassDemo():

    def test_methodA(self):
        # I would like to use the driver value here
        # How could I do this?
        # Something like this
        self.driver.get("https://www.google.com")
        self.driver.find_element(By.ID, "some id")
        print("Running method A")

    def test_methodB(self):
        print("Running method B")

Using self.driver fails with the error message

self = <test_class_demo.TestClassDemo object at 0x102fb6c18>

    def test_methodA(self):
>       self.driver.get("https://www.google.com")
E           AttributeError: 'TestClassDemo' object has no attribute 'driver'

I am aware that I can pass the fixture as an argument to every method where I want to use that, but that is not the best way because I need this in every method and it should be possible to pass it to the class and then use it in all the test methods.

What is the best way that I can make the driver object available to the methods?

EDIT 1:

Created the fixture in conftest.py like this as suggested

@pytest.yield_fixture(scope="class") # <-- note class scope
def oneTimeSetUp(request, browser): # <-- note the additional `request` param
    print("Running one time setUp")
    if browser == 'firefox':
        driver = webdriver.Firefox()
        driver.maximize_window()
        driver.implicitly_wait(3)
        print("Running tests on FF")
    else:
        driver = webdriver.Chrome()
        print("Running tests on chrome")

    ## add `driver` attribute to the class under test -->
    if request.cls is not None:
        request.cls.driver = driver
    ## <--

    yield driver
    print("Running one time tearDown")

I have one more class, which object in need in the TestClassDemo and I need to pass the same driver instance to the class. Consider it as class ABC

class ABC():

    def __init(self, driver):
        self.driver = driver

    def enterName(self):
        # Do something with driver instance

Then in the TestClassDemo

@pytest.mark.usefixtures("oneTimeSetUp", "setUp")
class TestClassDemo(unittest.TestCase):

    # I need to create an object of class ABC, so that I can use it here
    # abc = ABC(self.driver)

    @pytest.fixture(scope="class", autouse=True)
    def setup(self):
        self.abc = ABC(self.driver)
    # I tried this, but it's not working
    # This error message shows up
    # AttributeError: 'TestClassDemo' object has no attribute 'driver'

    def setup_module(self):
    self.abc = ABC(self.driver)
    # This also does not work
    # Error message ->  AttributeError: 'TestClassDemo' object has no attribute 'abc'


    def test_methodA(self):
        self.driver.get("https://google.com")
        self.abc.enterName("test")
        print("Running method A")

    def test_methodB(self):
        self.abc.enterName("test")
        print("Running method B")

This abc object should be usable in other test_ methods also.

All these classes are in separate modules, I mean to say in separate .py files.

Also please explain in the answer what is the best way to use instead of yield driver instance.

EDIT 2:

For this example without yield, what would be the best way to run oneTimeTearDown also? I was running the tearDown steps after the yield

@pytest.fixture(scope="class")
def oneTimeSetUp(request, browser):
    print("Running one time setUp")
    if browser == 'firefox':
        driver = webdriver.Firefox()
        driver.maximize_window()
        driver.implicitly_wait(3)
        print("Running tests on FF")
    else:
        driver = webdriver.Chrome()
        print("Running tests on chrome")

    if request.cls is not None:
        request.cls.driver = driver

Also I tried using UnitTest class, but when I use def setUpClass(cls), I was not able to use the objects instantiated in the test_ methods. So I couldn't not figure out how to achieve that.

I also wanted to provide command line arguments like browser from the command line and when I tried unittest, I had to write the command line argument in every class. I wanted to provide them in one place only, like a test suite. So conftest helped me here.

I had a question on stackoverflow but didn't get a response. Could you please take a look at that also? Python unittest passing arguments to parent test class

Thanks

Thanks

回答1:

There's a technique outlined in the py.text unittest integration documentation that may be helpful to you ... using the built-in request fixture. Otherwise, I'm not aware of way to access the return value of a fixture without providing the named fixture as a method param.

@pytest.yield_fixture(scope="class") # <-- note class scope
def oneTimeSetUp(request, browser): # <-- note the additional `request` param
    print("Running one time setUp")
    if browser == 'firefox':
        driver = webdriver.Firefox()
        print("Running tests on FF")
    else:
        driver = webdriver.Chrome()
        print("Running tests on chrome")

    ## add `driver` attribute to the class under test -->
    if request.cls is not None:
        request.cls.driver = driver
    ## <--

    yield driver
    print("Running one time tearDown")

Now you can access the driver as a class attribute in TestClassDemo, as you have in your example (i.e. self.driver should work).

The caveat is that your fixture must use scope='class', otherwise the request object will not possess a cls attribute.

I hope that helps!

---

UPDATE

I have one more class, which object in need in the TestClassDemo and I need to pass the same driver instance to the class. Consider it as class ABC

It's difficult to know without more context, but it seems to me that you can probably get away with instantiating an ABC object at the same time that you instantiate the driver ... in the oneTimeSetUp fixture. For example ...

@pytest.yield_fixture(scope="class")
def oneTimeSetUp(request, browser):
    print("Running one time setUp")
    if browser == 'firefox':
        driver = webdriver.Firefox()
        driver.maximize_window()
        driver.implicitly_wait(3)
        print("Running tests on FF")
    else:
        driver = webdriver.Chrome()
        print("Running tests on chrome")

    if request.cls is not None:
        request.cls.driver = driver
        request.cls.abc = ABC(driver) # <-- here

    yield driver
    print("Running one time tearDown")

But if you only need the ABC instance for a test class or two, here's how you might use a fixture inside the class definition ...

@pytest.mark.usefixtures("oneTimeSetUp", "setUp")
class TestClassDemo(unittest.TestCase):
    @pytest.fixture(autouse=True)
    def build_abc(self, oneTimeSetUp): # <-- note the oneTimeSetup reference here
        self.abc = ABC(self.driver)

    def test_methodA(self):
        self.driver.get("https://google.com")
        self.abc.enterName("test")
        print("Running method A")

    def test_methodB(self):
        self.abc.enterName("test")
        print("Running method B")

I wouldn't be particularly happy with the second example. A third option would be to have another yield_fixture, or similar, that is completely separate from oneTimeSetUp and returns an ABC instance with the driver already wrapped.

Which way is best for you? Not sure. You'll need to decide based on what you're working with.

It's proper to note for posterity that pytest fixtures are just sugar and a bit of magic. You are not required to use them at all, if you find them difficult. pytest is happy to execute vanilla unittest TestCases.

---

Also please explain in the answer what is the best way to use instead of yield driver instance.

Here's what I had in mind ...

@pytest.fixture(scope="class")
def oneTimeSetUp(request, browser):
    print("Running one time setUp")
    if browser == 'firefox':
        driver = webdriver.Firefox()
        driver.maximize_window()
        driver.implicitly_wait(3)
        print("Running tests on FF")
    else:
        driver = webdriver.Chrome()
        print("Running tests on chrome")

    if request.cls is not None:
        request.cls.driver = driver

... notice that this doesn't return (or yield) the driver object, which means that it's no longer useful to provide this fixture as a named parameter to a function/method, which should be fine if all of your test cases are written as classes (suggested by your examples).

However, if you want to use the fixture as a named parameter, don't do this.

来源：https://stackoverflow.com/questions/37760366/pytest-how-to-use-fixture-return-value-in-test-method-under-a-class