Disclaimer

Spaker only has written almost no test in his projects.

Installation of pytest

conda install pytest

or

pip install pytest

First test example

1. create a function with the test_ prefix

def inc(x):
    return x + 1


def test_answer():
    assert inc(3) == 4

2. Run the test

pytest
or
pytest -q test_simple.py 

File names and function names

• By default pytest only identifies the file names starting with test_ or ending with _test as the test files.
• Pytest requires the test method names to start with "test" .

Test Error Message

def inc(x):
    return x + 1


def test_answer():
    assert inc(3) == 5  # Error

Parameterized test

import pytest 

def add(x, y):
    return x + y

@pytest.mark.parametrize("x, y, z", [
    (1, 2, 3),
    (4, 5, 9),
    (3, 8, 12)  # pop error
])
def test_answer(x, y, z):
    print(x, y, z)
    assert add(x, y) == z

Skip

import pytest 

def add(x, y):
    return x + y

def test_func():
    assert 4 == 5

@pytest.mark.skip
@pytest.mark.parametrize("x, y, z", [
    (3, 8, 12)  # pop error
])
def test_add(x, y, z):
    assert add(x, y) == z

Conditional skip

import pytest 
import sys

def add(x, y):
    return x + y

@pytest.mark.skipif(sys.platform != 'win32', reason='Only run on win32')
def test_func():
    assert 4 == 5

@pytest.mark.parametrize("x, y, z", [
    (3, 8, 12)  # pop error
])
def test_add(x, y, z):
    assert add(x, y) == z

xfail (expected fail)

import pytest 

def add(x, y):
    return x + y

@pytest.mark.xfail
def test_func():
    assert 4 == 5

Fixture

• A software test fixture sets up the system for the testing process by providing it with all the necessary code to initialize it, thereby satisfying whatever preconditions there may be. (wikipedia)
• The purpose of test fixtures is to provide a fixed baseline upon which tests can reliably and repeatedly execute. (pytest doc)
• Dependency injection

Simple fixture example

import pytest

class DBConnection(object):
    def query(self, stmt):
        return [('a', 'b', 1), ('d', 'ff', 9)]

@pytest.fixture
def db():    
    return DBConnection()

def test_query(db):
    data = db.query('some stmt')
    # use here to check data property
    assert len(data[0]) == 4 

conftest.py

# conftest.py
import pytest

class DBConnection(object):
    def query(self, stmt):
        return [('a', 'b', 1), ('d', 'ff', 9)]

@pytest.fixture
def db():
    return DBConnection()

# test_answer.py
def test_query(db):
    data = db.query('some stmt')
    # use here to check data property
    assert len(data[0]) == 4 

conftest.py: sharing fixture functions

• Put fixtures into conftest.py, they will automatically included.
• conftest.py can include some settings.
• Every python package (a folder with init.py) can have their own conftest.py

conftest.py in main/sub directory

# __init__.py

# conftest.py
import pytest

class DBConnection(object):
    def query(self, stmt):
        return [('a', 'b', 1), ('d', 'ff', 9)]

@pytest.fixture(autouse=True)
def db():
    return DBConnection()

# test_answer.py
def test_query(db):
    data = db.query('some stmt')
    assert len(data[0]) == 4  # Pop error

conftest.py in main/sub directory

# subdir/__init__.py

# subdir/conftest.py
import pytest

class DBConnection(object):
    def query(self, stmt):
        return [('a', 'b', 1, 9), ('d', 'ff', 9, 11)]

@pytest.fixture(autouse=True)
def db():
    return DBConnection()

# subdir/test_answer.py
def test_query(db):
    data = db.query('some stmt')
    assert len(data[0]) == 3  # Pop error

2 errors!!

Scope of fixture

Scope of fixture

import pytest


@pytest.fixture(scope="session")
def resource_session(request):
    print('resource_session INIT')       
    request.addfinalizer(
        lambda: print('\nIn resource_session\'s end'))

@pytest.fixture(scope="module")
def resource_module(request):
    print('resource_module INIT')
    request.addfinalizer(
        lambda: print('\nIn resource_module\'s end'))

@pytest.fixture(scope="function")
def resource_func(request):
    print('resource_func INIT')
    request.addfinalizer(
        lambda: print('\nIn resource_func\'s end'))

Scope of fixture

# test_1_2.py
def test_one(resource_func):
    print('In test_one()')

def test_two(resource_module):
    print('\nIn test_two()')

# test_3_4.py
def test_three(
    resource_func,
    resource_session, 
    resource_module):
    print('\nIn test_three()')


def test_four(resource_func, resource_module):
    print('\nIn test_four()')

• Fixture method is called when the resource is needed.
• Resource given by the fixture is finalized according to fixture scope
• http://pythontesting.net/framework/pytest/pytest-session-scoped-fixtures/

fixture X fixture

# conftest.py
import pytest

@pytest.fixture(scope='module', params=['a', 'b'])
def resource_1(request):
    param = request.param
    return 'resource_1_' + param


@pytest.fixture(scope='module', params=['a', 'b'])
def resource_2(request):
    param = request.param
    return 'resource_2_' + param

fixture X fixture

# test_answer.py
def test_1(resource_1):
    print('In test_1: ' + resource_1)

def test_2(resource_2):
    print('In test_2: ' + resource_2)

def test_3(resource_1, resource_2):
    print('In test_3: ' + resource_1 + ', ' + resource_2)

fixture X fixture

configuration with conftest.py

# conftest.py
import pytest
import sys

def pytest_addoption(parser):
    parser.addoption(
        "--cmdopt", action="store", 
        default="type1", 
        help="my option: type1 or type2")

def pytest_configure(config):
    sys._called_from_test = 'True'

def pytest_unconfigure(config):
    del sys._called_from_test

def pytest_report_header(config):
    return "This is header"

@pytest.fixture
def cmdopt(request):
    return request.config.getoption("--cmdopt")

configuration with conftest.py

# test_answer.py
import argparse
import sys

def test_answer(cmdopt):
    print("sys._called_from_test: ", sys._called_from_test)
    if cmdopt == 'type1':
        print('first')
    elif cmdopt == 'type2':
        print('second')
    assert True

More detail please go to

• pytest example
• Pytest 還有他的快樂夥伴
• Introduction to py.test
• pytest ALL THE THINGS

Thank you!

Q&A