cats & dogs

example-optimized.py

from contextlib import contextmanager
import pytest

dogs = set()

@contextmanager
def expensive_operation_with_dog_named(name):
    print(f"expensive operation with dog named {name}")
    dogs.add(name)
    yield
    dogs.remove(name)


cats = set()

@contextmanager
def expensive_operation_with_cat_named(name):
    print(f"expensive operation with cat named {name}")
    cats.add(name)
    yield
    cats.remove(name)


@pytest.fixture(scope="class")
def charlie():
    with expensive_operation_with_dog_named("charlie"):
        yield


@pytest.fixture(scope="class")
def buddy():
    with expensive_operation_with_dog_named("buddy"):
        yield


@pytest.fixture()
def tom():
    with expensive_operation_with_cat_named("tom"):
        yield


@pytest.fixture()
def simba():
    with expensive_operation_with_cat_named("simba"):
        yield


class TestWithCharlie:
    def test_charlie_tom(self, charlie, tom):
        assert dogs == {"charlie"}
        assert cats == {"tom"}

    def test_charlie_simba(self, charlie, simba):
        assert dogs == {"charlie"}
        assert cats == {"simba"}

class TestWithBuddy:
    def test_buddy_tom(self, buddy, tom):
        assert dogs == {"buddy"}
        assert cats == {"tom"}

    def test_buddy_simba(self, buddy, simba):
        assert dogs == {"buddy"}
        assert cats == {"simba"}

class TestWithSimbaBeforeBuddy:
    @pytest.fixture(scope="function")
    def buddy(self):
        with expensive_operation_with_dog_named("buddy"):
            yield

    def test_simba_buddy(self, simba, buddy):
        assert dogs == {"buddy"}
        assert cats == {"simba"}

def test_tree():
    assert dogs == cats == set()


# example-optimized.py
#       SETUP    C charlie
#         SETUP    F tom
#         example-optimized.py::TestWithCharlie::test_charlie_tom (fixtures used: charlie, tom)
#         TEARDOWN F tom
#         SETUP    F simba
#         example-optimized.py::TestWithCharlie::test_charlie_simba (fixtures used: charlie, simba)
#         TEARDOWN F simba
#       TEARDOWN C charlie
#       SETUP    C buddy
#         SETUP    F tom
#         example-optimized.py::TestWithBuddy::test_buddy_tom (fixtures used: buddy, tom)
#         TEARDOWN F tom
#         SETUP    F simba
#         example-optimized.py::TestWithBuddy::test_buddy_simba (fixtures used: buddy, simba)
#         TEARDOWN F simba
#       TEARDOWN C buddy
#         SETUP    F simba
#         SETUP    F buddy
#         example-optimized.py::TestWithSimbaBeforeBuddy::test_simba_buddy (fixtures used: buddy, simba)
#         TEARDOWN F buddy
#         TEARDOWN F simba
#         example-optimized.py::test_tree

example.py

from contextlib import contextmanager
import pytest

dogs = set()

@contextmanager
def expensive_operation_with_dog_named(name):
    print(f"expensive operation with dog named {name}")
    dogs.add(name)
    yield
    dogs.remove(name)


cats = set()

@contextmanager
def expensive_operation_with_cat_named(name):
    print(f"expensive operation with cat named {name}")
    cats.add(name)
    yield
    cats.remove(name)


@pytest.fixture()
def charlie():
    with expensive_operation_with_dog_named("charlie"):
        yield


@pytest.fixture()
def buddy():
    with expensive_operation_with_dog_named("buddy"):
        yield


@pytest.fixture()
def tom():
    with expensive_operation_with_cat_named("tom"):
        yield


@pytest.fixture()
def simba():
    with expensive_operation_with_cat_named("simba"):
        yield


def test_charlie_tom(charlie, tom):
    assert dogs == {"charlie"}
    assert cats == {"tom"}

def test_charlie_simba(charlie, simba):
    assert dogs == {"charlie"}
    assert cats == {"simba"}

def test_buddy_tom(buddy, tom):
    assert dogs == {"buddy"}
    assert cats == {"tom"}

def test_buddy_simba(buddy, simba):
    assert dogs == {"buddy"}
    assert cats == {"simba"}

def test_simba_buddy(simba, buddy):
    assert dogs == {"buddy"}
    assert cats == {"simba"}

def test_tree():
    assert dogs == cats == set()


# example.py
#         SETUP    F charlie
#         SETUP    F tom
#         example.py::test_charlie_tom (fixtures used: charlie, tom)
#         TEARDOWN F tom
#         TEARDOWN F charlie
#         SETUP    F charlie
#         SETUP    F simba
#         example.py::test_charlie_simba (fixtures used: charlie, simba)
#         TEARDOWN F simba
#         TEARDOWN F charlie
#         SETUP    F buddy
#         SETUP    F tom
#         example.py::test_buddy_tom (fixtures used: buddy, tom)
#         TEARDOWN F tom
#         TEARDOWN F buddy
#         SETUP    F buddy
#         SETUP    F simba
#         example.py::test_buddy_simba (fixtures used: buddy, simba)
#         TEARDOWN F simba
#         TEARDOWN F buddy
#         SETUP    F simba
#         SETUP    F buddy
#         example.py::test_simba_buddy (fixtures used: buddy, simba)
#         TEARDOWN F buddy
#         TEARDOWN F simba
#         example.py::test_tree

module-level-bad.py

import pytest

@pytest.fixture(scope="module")
def cat():
    yield "cat"

def test_cat_0(cat):
    assert 1

def test_cat_1():
    assert 1


# $ python -m pytest module-level-bad.py --setup-plan

# module-level-bad.py
#     SETUP    M cat
#         module-level-bad.py::test_cat_0 (fixtures used: cat)
#         module-level-bad.py::test_cat_1
#     TEARDOWN M cat

# $ python -m pytest module-level-bad.py -k 1 --setup-plan

# module-level-bad.py
#         module-level-bad.py::test_cat_1

proposed-solution.py

from contextlib import contextmanager
import pytest

dogs = set()

@contextmanager
def expensive_operation_with_dog_named(name):
    print(f"expensive operation with dog named {name}")
    dogs.add(name)
    yield
    dogs.remove(name)


cats = set()

@contextmanager
def expensive_operation_with_cat_named(name):
    print(f"expensive operation with cat named {name}")
    cats.add(name)
    yield
    cats.remove(name)


@pytest.fixture(scope="only the tests that use this fixture")
def charlie():
    with expensive_operation_with_dog_named("charlie"):
        yield


@pytest.fixture(scope="only the tests that use this fixture")
def buddy():
    with expensive_operation_with_dog_named("buddy"):
        yield


@pytest.fixture(scope="only the tests that use this fixture")
def tom():
    with expensive_operation_with_cat_named("tom"):
        yield


@pytest.fixture(scope="only the tests that use this fixture")
def simba():
    with expensive_operation_with_cat_named("simba"):
        yield


def test_charlie_tom(charlie, tom):
    assert dogs == {"charlie"}
    assert cats == {"tom"}

def test_charlie_simba(charlie, simba):
    assert dogs == {"charlie"}
    assert cats == {"simba"}

def test_buddy_tom(buddy, tom):
    assert dogs == {"buddy"}
    assert cats == {"tom"}

def test_buddy_simba(buddy, simba):
    assert dogs == {"buddy"}
    assert cats == {"simba"}

def test_simba_buddy(simba, buddy):
    assert dogs == {"buddy"}
    assert cats == {"simba"}

def test_tree():
    assert dogs == cats == set()


# setup plan

# setup charlie
#   setup tom
#     test_charlie_tom
#   teardown tom
#   setup simba
#     test_charlie_simba
#   teardown simba
# teardown charlie
# setup buddy
#   setup tom
#     test_buddy_tom
#   teardown tom
#   setup simba
#     test_buddy_simba
#   teardown simba
# teardown buddy
# setup simba
#   setup buddy
#     test_simba_buddy
#   teardown buddy
# teardown simba
# test_tree