pytest fixtures¶Required boilerplate for using pytest inside notebooks.
# Let's make sure pytest and ipytest packages are installed
# ipytest is required for running pytest inside Jupyter notebooks
import sys
!{sys.executable} -m pip install pytest 'ipytest>=0.3.0'
import pytest
from ipytest import magics, clean_tests
__file__ = 'pytest_fixtures.ipynb'
Similarly as you can parametrize test functions with pytest.mark.parametrize, you can parametrize fixtures:
PATHS = ['/foo/bar.txt', '/bar/baz.txt']
@pytest.fixture(params=PATHS)
def executable(request):
return request.param
%%run_pytest[clean] '-s'
def test_something_with_executable(executable):
print(executable)
pytest.mark.usefixtures¶pytest.mark.usefixtures is useful especially when you want to use some fixture in a set of tests but you don't need the return value of the fixture.
@pytest.fixture
def my_fixture():
print('\nmy_fixture is used')
@pytest.fixture
def other_fixture():
return 'FOO'
%%run_pytest[clean] '-s'
@pytest.mark.usefixtures('my_fixture')
class TestMyStuff:
def test_somestuff(self):
pass
def test_some_other_stuff(self, other_fixture):
print('here we use also other_fixture which returns: {}'.format(other_fixture))
pass
# Needed to clean up test classes (Test*) in ipytest
clean_tests('Test*')
pytest built-in fixtures¶Here are a couple of examples of the useful built-in fixtures, you can view all available fixtures by running pytest --fixtures.
monkeypatch¶Built-in monkeypatch fixture lets you e.g. set environment variables and set/delete attributes of objects. The use cases are similar as with patching/mocking with unittest.mock.patch/unittest.mock.MagicMock which are part of the Python Standard Library.
Monkeypatching environment variables:
import os
def get_env_var_or_none(var_name):
return os.environ.get(var_name, None)
%%run_pytest[clean] '-s'
def test_get_env_var_or_none_with_valid_env_var(monkeypatch):
monkeypatch.setenv('MY_ENV_VAR', 'secret')
res = get_env_var_or_none('MY_ENV_VAR')
assert res == 'secret'
def test_get_env_var_or_none_with_missing_env_var():
res = get_env_var_or_none('NOT_EXISTING')
assert res is None
Monkeypatching attributes:
class SomeClass:
some_value = 'some value'
@staticmethod
def tell_the_truth():
print('This is the original truth')
def fake_truth():
print('This is modified truth')
@pytest.fixture
def fake_some_class(monkeypatch):
monkeypatch.setattr('__main__.SomeClass.some_value', 'fake value')
monkeypatch.setattr('__main__.SomeClass.tell_the_truth', fake_truth)
%%run_pytest[clean] '-s'
def test_some_class(fake_some_class):
print(SomeClass.some_value)
SomeClass.tell_the_truth()
def word_count_of_txt_file(file_path):
with open(file_path, 'r') as f:
content = f.read()
return len(content.split())
%%run_pytest[clean] '-s'
def test_word_count(tmpdir):
test_file = tmpdir.join('test.txt')
test_file.write('This is example content of seven words')
res = word_count_of_txt_file(str(test_file)) # str returns the path
assert res == 7
# scope is function also by default
@pytest.fixture(scope='function')
def func_fixture():
print('\nfunc')
@pytest.fixture(scope='module')
def module_fixture():
print('\nmodule')
@pytest.fixture(scope='session')
def session_fixture():
print('\nsession')
%%run_pytest[clean] '-s'
def test_something(func_fixture, module_fixture, session_fixture):
pass
def test_something_else(func_fixture, module_fixture, session_fixture):
pass
@pytest.fixture
def some_fixture():
print('some_fixture is run now')
yield 'some magical value'
print('\nthis will be run after test execution, you can do e.g. some clean up here')
%%run_pytest[clean] '-s'
def test_something(some_fixture):
print('running test_something')
assert some_fixture == 'some magical value'
print('test ends here')
@pytest.fixture(autouse=True)
def my_fixture():
print('\nusing my_fixture')
%%run_pytest[clean] '-s'
def test_1():
pass
def test_2():
pass