Python Pair Programming and TDD

Pair Programming and TDD

Slides

slides

Parts of the session

Introduction to Testing in Python. (10 min)
Pair programming a project using TDD.(80 min)
Switching pairs to explain the solution to each other. (30 min)
Retrospective. (30 min)

Goals

Improve our way of software development.
Experiment with TDD.
Experiment with Pair Programming.

Module to test


def div(x, y):
    return x / y

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

Test the module

import mymath

def test_div():
    assert mymath.div(6, 3)  == 2
    assert mymath.div(42, 2) == 21
 
def test_add():
    assert mymath.add(2, 2)  == 4
    assert mymath.add(0, 0) == 0

Running Pytest

pytest test_mymath.py

========= test session starts ==========
platform darwin -- Python 3.6.3, pytest-3.3.0, py-1.5.2, pluggy-0.6.0
rootdir: ../python-pair-programming-and-tdd-workshop/test, inifile:
plugins: cov-2.5.1
collected 2 items

test_mymath.py ..                                    [100%]

======= 2 passed in 0.02 seconds =======

Test the module even more

import mymath

def test_div():
    assert mymath.div(6, 3)  == 2
    assert mymath.div(42, 2) == 21
 
def test_add():
    assert mymath.add(2, 2)  == 4
    assert mymath.add(0, 0) == 0
    assert mymath.add(-1, 1) == 0
    assert mymath.add(19, 23) == 42

Running Pytest

pytest test_mymath_more.py

========= test session starts ==========
platform darwin -- Python 3.6.3, pytest-3.3.0, py-1.5.2, pluggy-0.6.0
rootdir: ../python-pair-programming-and-tdd-workshop/test, inifile:
plugins: cov-2.5.1
collected 2 items

test_mymath_more.py .F                               [100%]

=============== FAILURES ===============
_______________ test_add _______________

    def test_add():
        assert mymath.add(2, 2)  == 4
        assert mymath.add(0, 0) == 0
>       assert mymath.add(-1, 1) == 0
E       assert -1 == 0
E        +  where -1 = <function add at 0x102386400>(-1, 1)
E        +    where <function add at 0x102386400> = mymath.add

test_mymath_more.py:10: AssertionError
====== 1 failed, 1 passed in 0.11 seconds ======

Pytest Coverage

pip install pytest-cov
pytest --cov=my --cov-report html --cov-branch
Open htmlcov/index.html

Learning Pytest

TDD - Test Driven Development

Write test first. It fails.
Implement code. Test passes.
Run test with coverage and check if there are cases that you have not covered yet.
Git commit

Why in pairs?

Learn from each other.
Learn how to express our ideas.
Continuous peer review.
Better solutions.
Less bugs.
You already know how to program alone. Let's try something else now.

Pair Programming

There is no single right way to do it. Experiment!
Verbalize everything
Driver - Navigator
Driver - Navigator - Observer

Llewellyn's Strong Style Pairing

"For an idea to go from your head into the computer it MUST go through someone else's hands."
Llewellyn's strong-style pairing

Llewellyn's Strong Style Pairing: Driver

"Trust your navigator"
"Become comfortable working with incomplete understanding"
"What if I have an idea I want to implement?" - switch!

Llewellyn's Strong Style Pairing: Navigator

"Give the next instruction to the driver the instant they are ready to implement it."
"Talk in the highest level of abstraction the driver can understand."

Tic-tac-toe

Tic-tac-toe

tic-tac-toe.png

Tic-tac-toe - hints

Decide on a representation of the board.
Allow the computer to recognize when someone won.
Report invalid boards?
Allow two humans to play.
Make the computer play.
Make the system play against itself.
Watch War Games.

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Python Pair Programming and TDD