Basics

Basics

import pytest

def test_a():
    assert 1 != 2

class TestB:
    def test_b(self):
        assert 'a'.upper() == 'A'

    def test_c(self):
        with pytest.raises(ZeroDivisionError):
            1/0
            

Fixtures

Fixture

import random

@pytest.fixture
def rnd():
    return random.random()
            

def test_rnd(rnd):
    print(rnd)
            

Fixture dependencies

@pytest.fixture
def rnd_gen():
    return random.Random(123456)


@pytest.fixture
def rnd(rnd_gen):
    return rnd_gen.random()
            

Fixture calculation

@pytest.fixture
def fixture_a(rnd):
    return rnd

@pytest.fixture
def fixture_b(rnd):
    return rnd

def test(fixture_a, fixture_b):
    assert fixture_a == fixture_b  # ???
            

Fixture factories

@pytest.fixture
def make_rnd(rnd_gen):
    def maker()
        return rnd_gen.random()
    return maker
            

@pytest.fixture
def fixture_a(rnd):
    return rnd()

@pytest.fixture
def fixture_b(rnd):
    return rnd()

def test(fixture_a, fixture_b):
    assert fixture_a == fixture_b  # ???
              

Resource cleanup

@pytest.yield_fixture
def opened_file():
    f = open("filename")
    try:
        yield f
    finally:
        f.close()
            

def test_a(opened_file):
    assert opened_file.read() == "file content"
            

Cleanup for factories

@pytest.yield_fixture
def open_file():
    f = None
    def opener(filename):
        nonlocal f
        assert f is None
        f = open(filename)
        return f
    yield opener
    if f is not None:
        f.close()
            

def test_a(open_file):
    assert open_file("file_a.txt").read() == "Content A"
    assert open_file("file_b.txt").read() == "Content B"
            

Comparison with unittest

Monolithic test case

class TestA(unittest.TestCase):
    def setUp(self):
        self.redis = redis.Redis()
        self.db = db.connect(':memory:')

    def tearDown(self):
        self.redis.close()
        self.db.close()

    def test_a(self):
        self.db.execute(...)
        self.redis.set(...)
            

Mixin classes

class RedisMixin:
    def setUp(self):
        self.redis = Redis()
        super().setUp()
    def tearDown(self):
        self.redis.close()
        super().tearDown()

class DBMixin:
    def setUp(self):
        self.db = sqlite3.connect(':memory:')
        super().setUp()
    def tearDown(self):
        self.db.close()
        super().tearDown()
            

class TestA(RedisMixin, DBMixin, unittest.TestCase):
    def setUp(self):
        self.val = 'value'
        super().setUp()

    def tearDown(self):
        ...
        super().tearDown()

    def test_a(self):
        self.db.execute(...)
        self.redis.set(...)
            

py.test

@pytest.yield_fixture
def redis():
    with Redis() as redis:
        yield redis

@pytest.yield_fixture
def db():
    with sqlite3.connect(':memory:') as db:
        yield db

def test_a(db, redis):
    db.execute(...)
    redis.set(...)
            

Transactions

@pytest.yield_fixture
def transaction(db):
    cursor = db.cursor()
    try:
       yield cursor
       db.commit()
    except:
       db.rollback()
            

def test_b(transaction):
    transaction.execute("INSERT INTO tbl(name) VALUES ('John')")
    raise RuntimeError("Error text")
    transaction.execute("INSERT INTO tbl(name) VALUES ('Mary')")
            

Project structure

• root
• project
• __init__.py
• ...
• tests
• conftest.py
• redis_fixtures.py
• db_fixtures.py
• test_a.py
• setup.py

No __init__.py in tests folder

conftest.py

import pytest

pytest_plugins = ['redis_fixtures', 'db_fixtures']

@pytest.fixture
def fixture_a():
    return 'value'
            

No fixture imports in conftest.py

Docker and tests

Fixture scope

• function
• class
• module
• session

Unique ID and docker client

import docker as libdocker

@pytest.fixture(scope='session')
def session_id():
    return str(uuid.uuid4())
@pytest.fixture(scope='session')
def unused_port():
    def f():
        with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
            s.bind(('127.0.0.1', 0))
            return s.getsockname()[1]
    return f
@pytest.fixture(scope='session')
def docker():
    return libdocker.Client(version='auto')
            

Running container

@pytest.yield_fixture(scope='session')
def redis_server(unused_port, session_id, docker):
    docker.pull('redis')
    port = unused_port()
    container = docker.create_container(
        image='redis',
        name='test-redis-{}'.format(session_id),
        ports=[6379], detach=True,
        host_config=docker.create_host_config(
            port_bindings={6379: port}))
    docker.start(container=container['Id'])
    ping_redis(port)  # N.B.
    container['redis_port'] = port
    yield container
    docker.kill(container=container['Id'])
    docker.remove_container(container['Id'])
            

Ping Redis

def ping_redis(port)
    timeout = 0.001
    for i in range(100):
        try:
            client = redis.StrictRedis(host='127.0.0.1',
                                       port=port, db=0)
        except redis.ConnectionError:
            time.sleep(timeout)
            timeout *= 2
        else:
            client.close()
    else:
        raise RuntimeError("Cannot connect to redis")
            

Redis client

@pytest.yield_fixture
def redis_client(redis_server):
    client = redis.StrictRedis(host='127.0.0.1',
                               port=redis_server['redis_port'],
                               db=0)
    yield client
    client.flushdb()
    client.close()
            

Test

def test_redis(redis_client):
    redis_client.set(b'key', b'value')
    assert redis_client.get(b'key') == b'value'
            

Plugins

Test skipping

@pytest.mark.skipif(sys.version_info < (3, 4, 1),
                    reason="Python<3.4.1 doesnt support "
                           "__del__ calls from GC")
def test___del__():
    ...
            

Test exclusion

def pytest_ignore_collect(path, config):
    if 'py35' in str(path):
        if sys.version_info < (3, 5, 0):
            return True
            

• tests
• conftest.py
• ...
• py35
• test_1.py
• test_2.py