Introduction to TDD using python

TDD
(Test Driven Development)

"approach to development which combines test-first development where you write a test before you write just enough production code to fulfill that test and refactoring.

“The act of writing a unit test is more an act of design than of verification. It is also more an act of documentation than of verification. The act of writing a unit test closes a remarkable number of feedback loops, the least of which is the one pertaining to verification of function” - Robert C. Martin

Traditional software process

Design

Implement

Test

Traditional software process

Issues

Long phase execution
Manual testing
Lost or regression bugs
The bigger the codebase the longer the time to test and more probability to break things

TDD Flow

Test / Design

Implement

Benefits

Much less regression test bugs
Drastically reduced time to identify issues
Easy refactoring verification.
Better software design.

Python testing tools

Unittest

Doctest

py.test

Nose
Tox
Unittest2
Mock

Lets see some code

import unittest
from operations.operations import factorial, summation


class TddInPythonExample(unittest.TestCase):

    def test_factorial_operation_returns_correct_result(self):
        result = factorial(2)
        self.assertEqual(2, result)

    def test_summation_operation_returns_correct_result(self):
        result = summation(2)
        self.assertEqual(3, result)

test_operations.py

# coding=utf-8


def factorial(number):
    return 0


def summation(number):
    return 0

operations.py

/usr/bin/python /Applications/PyCharm.app/Contents/helpers/pydev/pydevd.py --multiproc 
--qt-support --client 127.0.0.1 --port 64753 --file /Applications/PyCharm.app/Contents
/helpers/pycharm/utrunner.py /Users/jhonjairoscalablepath/PycharmProjects/
python-lettuce-sample-2/tests/test_operations.py::TddInPythonExample::
test_summation_operation_returns_correct_result true
Testing started at 4:42 PM ...
pydev debugger: process 55353 is connecting
Connected to pydev debugger (build 143.1919)


Failure
Traceback (most recent call last):
  File "/Users/jhonjairoscalablepath/PycharmProjects/python-lettuce-sample-2/tests
/test_operations.py", line 13, in test_summation_operation_returns_correct_result
    self.assertEqual(3, result)
AssertionError: 3 != 0


Process finished with exit code 0

Test fail !!! :(

Don't be sad!

Now you have things to do :D

operations.py

# coding=utf-8


def factorial(number):
    number = int(number)
    if (number == 0) or (number == 1):
        return 1
    else:
        return number*factorial(number-1)


def summation(number):
    number = int(number)
    if number == 0:
        return 0
    else:
        return number+summation(number-1)

/usr/bin/python /Applications/PyCharm.app/Contents/helpers/pydev/pydevd.py --multiproc 
--qt-support --client 127.0.0.1 --port 64816 --file /Applications/PyCharm.app/
Contents/helpers/pycharm/utrunner.py /Users/jhonjairoscalablepath/PycharmProjects/
python-lettuce-sample-2/tests/test_operations.py::TddInPythonExample::
test_summation_operation_returns_correct_result true
Testing started at 4:45 PM ...
pydev debugger: process 55376 is connecting

Connected to pydev debugger (build 143.1919)

Process finished with exit code 0

Test pass !!! :'D

ATDD
(Acceptance Test Driven Development)

is a communication tool between the customer, developer, and tester to ensure that the requirements are well-defined

"Customer"

or
Product Owner

Tester

Developer

requirements written as acceptance tests

focus on writing acceptance tests before developers begin coding

"the product owner, customer or domain expert is able to specify new functionality by writing new acceptance tests or test cases, without needing to consult developers"

http://guide.agilealliance.org/guide/atdd.html