@__omar__

• Backend lead at Playlab Games
• Python developer for the last 6 years
• Mainly django, some web crawling and machine learning too

Testing

Why test?

• Catch regressions
• Clarify your designs
• Improve code quality
• Make life easier for new developers
• You're doing it anyway

Testing pyramid

from rubyplus.com

Testing in python

Testing in python

• doctest
• unittest
• nose
• pytest

doctest

def square(x):
    """
    Squares x.

    >>> square(2)
    4
    >>> square(-2)
    4
    """
    return x * x

if __name__ == '__main__':
    import doctest
    doctest.testmod()

from python-guide.org

doctest

Success - no output

Failure:

**********************************************************************
File "tests.py", line 5, in __main__.square
Failed example:
    square(2)
Expected:
    4
Got:
    3
**********************************************************************

doctest

• In the stdlib
• Good for simple unit tests
• Makes great documentation
• Not enough on its own

unittest

import unittest

def square(x):
    return x * x

class MyTest(unittest.TestCase):
    def setUp(self):
        # Do some setup
        pass

    def test_square(self):
        self.assertEqual(square(2), 4)
        self.assertEqual(square(-2), 4)

    def tearDown(self):
        # Tear everything down
        pass

if __name__ == '__main__':
    unittest.main()

unittest

Success:

.
----------------------------------------------------------------------
Ran 1 test in 0.000s

OK

Failure:

F
======================================================================
FAIL: test_square (__main__.MyTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "tests.py", line 12, in test_square
    self.assertEqual(square(2), 4)
AssertionError: 3 != 4

----------------------------------------------------------------------
Ran 1 test in 0.000s

FAILED (failures=1)

unittest

• In the stdlib
• De-facto standard
• Direct port of JUnit
• Powerful but unpythonic

pytest

def square(x):
    return x * x

def test_square():
    assert square(2) == 4
    assert square(-2) == 4

$ py.test tests.py

================================================ test session starts =================================================
platform darwin -- Python 2.7.9 -- py-1.4.26 -- pytest-2.7.0
rootdir: /Users/omar/dev/presentations, inifile:
collected 1 items

tests.py .

============================================== 1 passed in 0.01 seconds ==============================================

pytest

Failure:

================================================ test session starts =================================================
platform darwin -- Python 2.7.6 -- py-1.4.26 -- pytest-2.7.0
rootdir: /Users/omar/dev/presentations, inifile:
collected 1 items

tests.py F

====================================================== FAILURES ======================================================
____________________________________________________ test_square _____________________________________________________

    def test_square():
>       assert square(2) == 4
E       assert 3 == 4
E        +  where 3 = square(2)

tests.py:5: AssertionError
============================================== 1 failed in 0.01 seconds ==============================================

pytest

• Has been around forever
• Simple, clean, pythonic

Fixtures

import os
import pytest

def exp(x):
    return x ** int(os.environ['EXPONENT'])

@pytest.fixture
def square():
    os.environ['EXPONENT'] = '2'

def test_exp(square):
    assert exp(2) == 4
    assert exp(-2) == 4

Discovery

• Suffix each test file with _test.py
• Run py.test

Examples

• flask