Fixture demo

fixtures.py

"""Pytest fixtures
Fixtures give you a convenient way to perform setup actions outside of a test.
By limiting or expanding the scope of a fixture, you can cut down on costly setup tasks.
"""
import pytest
import random
import unittest2  # please never


NUM = "0123456789"
ALPHA = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"


def dummy(val):
    """This is the target of our tests (ideally in a separate file)"""
    return int(val) * 5

"""pytest searches for these next two named methods in each file.
if present, setup_module will run before tests are ran
teardown_module will run after
you don't need to do anything special to trigger this
"""
def setup_module(module):
    print("==================== Setting things up ====================")


def teardown_module(module):
    print("==================== Tearing things down ====================")


@pytest.fixture
def good_int():
    """The most basic fixture. This will provide a new value for each test."""
    return random.randint(0, 100)


@pytest.fixture
def good_str():
    """By default, a fixture's scope is at the test/function level.
    This means that random return values will be different for each test
    """
    res = ""
    for i in range(5):
        res += random.choice(NUM)
    return res


@pytest.fixture(scope="module")
def bad_str():
    """To share a common random value (or object), set the scope to module.
    Each test in this file, accepting bad_str will then have the same value
    """
    res = ""
    for i in range(5):
        res += random.choice(ALPHA)
    return res


@pytest.fixture(scope="session")
def common_int():
    """A scope of session will use the same value for all tests in the same pytest run"""
    return random.randint(0, 100)


@pytest.fixture(scope="module")
def important_thing():
    """If things don't go well during a fixture, you can skip any test that expects a value."""
    thing = random.choice([True, False])
    if not thing:
        # I don't want to get a false failure, so skip dependent tests
        pytest.skip("Setup failed. Skipping test...")
    return thing


@pytest.fixture(scope="class")
def my_cool_thing(request, bad_str):
    """You can even add attributes to a test class (unittest style) using fixtures
    note that this fixture also takes in the value of another fixture!
    """
    request.cls.my_thing = bad_str
    # tests in the class can then reference the value with: self.my_thing


def test_positive_dummy():
    """basic test. uses no fixtures"""
    assert dummy(5) == 25


def test_positive_dummy_int(common_int):
    """Experiement with switching common_int to good_int, then check output"""
    print(common_int)
    result = dummy(common_int)
    assert result == common_int * 5


def test_positive_dummy_int2(common_int):
    """Experiement with switching common_int to good_int, then check output"""
    print(common_int)
    result = dummy(common_int)
    assert result == common_int * 5


def test_positive_dummy_str(good_str):
    print(good_str)
    result = dummy(good_str)
    assert isinstance(result, int)


def test_negative_dummy_str(bad_str):
    print(bad_str)
    try:
        result = dummy(good_str)
        assert not isinstance(result, int)
    except:
        assert True


def test_positive_thing(important_thing):
    """This test has a 50% chance of being skipped"""
    assert important_thing


# broken, but you can play around with it
@pytest.mark.usefixtures("my_cool_thing")
class UnittestSucks(unittest2.TestCase):
    """Use pytest.mark.usefixtures to accept the previously define class-scoped fixture"""
    def __init__(self, *args, **kwargs):
        print(args)
        print(kwargs)
        self.whatever = "sure"

    def test_dont_use_unittest(self):
        print(self.my_thing)
        assert self.my_thing != self.whatever

run with pytest -sv fixtures.py for the best experience