how to make a python test driven development environment¶

This is one way to make a Python Test Driven Development environment

requirements¶

download and install Python
get an Integrated Development Environment (IDE). Here are a few options

windows requirements¶

If you are using a Windows computer, try

how to install Windows Subsystem Linux on Windows
If installing Windows Subsystem Linux does not work, you can use how to make a python test driven development environment on Windows without Windows Subsystem Linux instead

linux/Windows Subsystem Linux requirements¶

Attention

Do this only if you are using Linux or Windows Subsystem Linux

Open a terminal then type this to update the Linux package manager

sudo apt update

type this in the terminal to install Python

sudo apt install python3 python3-venv --yes

how to manually make a python test driven development environment¶

Imagine I have to work on a project and its name is magic. I open a terminal in the Integrated Development Environment (IDE) and use mkdir
```
mkdir magic
```
this makes a folder/directory for the project where its files will stay
I use cd
```
cd magic
```
this changes directory to the magic folder/directory I just made
I make a child folder/directory for the source code (the actual program)
```
mkdir src
```
I use touch
```
touch src/magic.py
```
this makes an empty file for the source code (the actual program)
I make a child folder/directory
```
mkdir tests
```
this is where I will add tests for the project
I use touch to add an empty file called __init__.py in the tests folder

Attention

make sure to use 2 underscores (__) for __init__.py
```
touch tests/__init__.py
```
this tells Python that tests is a python package, it will help it find the tests I write later
I use touch to add one more empty file in the tests directory for the actual test
```
touch tests/test_magic.py
```
Tip

I can use any name for the test file as long as it starts with test_

these are the folders/directories and files in the project

magic
├── src
│   └── magic.py
└── tests
    ├── __init__.py
    └── test_magic.py

.py at the end of a file name shows it is a Python module

test_failure¶

The Test Driven Development cycle is RED GREEN REFACTOR

RED: make it fail - write a failing test to make sure the test works
GREEN: make it pass - write only what is needed to make the failing test pass
REFACTOR: make it better - remove duplication

red: make it fail¶

I click on magic/tests/test_magic.py in the Integrated Development Environment (IDE) to open it in the editor, then type the following

Note

the line numbers below are a guide, you do not need to copy them
```
1import unittest
2
3
4class TestMagic(unittest.TestCase):
5
6    def test_failure(self):
7        self.assertFalse(True)
```
Here is an explanation of the code in the file
- import unittest imports the unittest module from the python standard library, it is used for testing
- class TestMagic
  - class is the Python keyword for making classes, which are a group of attributes and methods that belong together, see classes for more
  - TestMagic is the name of this class and will hold the test
    
    Tip
    
    I can use any name for the test class as long as it starts with Test
  - unittest.TestCase is a class from the unittest module which has methods for testing
  - class TestMagic(unittest.TestCase) defines TestMagic as a “child” of unittest.TestCase which means I can use its methods and attributes
- def test_failure
  - def is the Python keyword for making methods (functions), see functions for more
  - test_failure is the name of this method for my tests
    
    Tip
    
    I can use any name for the test method as long as it starts with test_
  - self. allows me to use attributes and methods of the TestMagic class which is a “child” of the unittest.TestCase class, instead of using TestMagic(). or unittest.TestCase().
  - self.assertFalse(True) is an assertion
    - assertFalse is a method in the unittest.TestCase class that checks if its input is False
    - True is given as the input
    I expect this line to fail because True is not False. If it does not fail, then Python and I have a problem
I turn on the Auto Save feature in the Integrated Development Environment (IDE) to automatically save files when I make a change so I do not repeat myself by hitting save (ctrl+s (windows/linux) or command+s (mac)) every time

I type this in the terminal to run the test

python3 -m unittest

the terminal shows AssertionError

F
=============================================================
FAIL: test_failure (tests.test_magic.TestMagic.test_failure)
-------------------------------------------------------------
Traceback (most recent call last):
  File ".../magic/tests/test_magic.py", line 7, in test_failure
    self.assertFalse(True)
    ~~~~~~~~~~~~~~~~^^^^^^
AssertionError: True is not false

-------------------------------------------------------------
Ran 1 test in A.XYZs

FAILED (failures=1)

If you are typing along, CONGRATULATIONS! You just wrote a test.

This is the RED part of the Test Driven Development cycle. The message in the terminal is about the failure, I like to read these from the bottom up, here is an explanation of each line

FAILED (failures=1) the number of failures
Ran 1 test in A.XYZs the number of tests it ran and how long they took
AssertionError: True is not false the Error/Exception raised and its message, in this case AssertionError is raised because True is not False
self.assertFalse(True) the line of code that caused the failure
~~~~~~~~~~~~~~~~^^^^^^ points to the part of the line above it that it thinks caused the error
File ".../magic/tests/test_magic.py", line 7, in test_failure the line number of the code that caused the failure and the location of the file where it is

Tip

Hold ctrl (windows/linux) or option (mac) on the keyboard and use the mouse to click on File ".../magic/tests/test_magic.py", line 7 in the terminal, and the Integrated Development Environment (IDE) will open the file in the editor with the cursor at the line where the failure happened
Traceback (most recent call last): all the information shown after this line that is indented to the right shows the calls that led to the failure, this is why I like to read it from the bottom up
FAIL: test_failure (tests.test_magic.TestMagic.test_failure) is a header with information in dot notation about the failing test method
- tests.test_magic.TestMagic.test_failure is the location of the failing test
- tests is the tests folder
- test_magic is the test_magic.py file
- TestMagic is the class defined on line 4
- test_failure is the method defined on line 6
F shows a failure
python3 -m unittest is the command to run tests with the unittest module
- python3 is the Python program
- -m is an option/switch passed to Python to run the module given after it

I recommend you keep a list of Errors/Exceptions you meet to become familiar with them, it helps when you run into them later. I add AssertionError to the list

import unittest

class TestMagic(unittest.TestCase):

    def test_failure(self):
        self.assertFalse(True)

# Exceptions Encountered
# AssertionError

green: make it pass¶

I change the input on line 7 from True to False

self.assertFalse(False)

then I run the test again in the terminal

python3 -m unittest

and the test passes! The terminal shows

.
------------------------------------------------------
Ran 1 test in A.XYZs

OK

cue CELEBRATION MUSIC AND DANCE! I am GREEN.

refactor: make it better¶

I ran python3 -m unittest to see the test fail, I ran python3 -m unittest again to see the test pass. I will have to run python3 -m unittest again when I make a code change, to make sure tests that were passing are not failing and that the new code I add does what I expect.

This means I have to run python3 -m unittest for each part of the Test Driven Development cycle or any time there is a code change. I do not want to type python3 -m unittest again, it is better for a program to run the tests so I do not repeat myself.

how to automatically run tests¶

how to make a virtual environment¶

I make a virtual environment with the venv module
```
python3 -m venv .venv
```
- python3 is the Python program
- -m is an option passed to Python to run the module given after the option as a script
- venv is a module from the python standard library, it is used to make a virtual environment with a given name.
- A virtual environment is a separate folder where python packages needed by the project will be installed, this helps me keep things that belong to the project in one place separate from other things on the computer
- .venv is the name given
  
  Note
  
  .venv is Python convention, I can use any name I want for the virtual environment
I activate the virtual environment to use it
```
source .venv/bin/activate
```
the (.venv) on the far left of the command line in the terminal shows that I am in the virtual environment, for example
```
(.venv) .../magic $
```
I upgrade pip the python package manager to the latest version
```
python3 -m pip install --upgrade pip
```
- pip is a module from the python standard library, it is used to install python packages
- install is an argument given to pip to install a given package name
- --upgrade is an option/switch given to the install argument for pip to upgrade the version of the given python package
- pip is the package name I am giving pip to install, in this case it upgrades itself
I use pip to see what packages are installed in the virtual environment
```
pip list
```
the terminal shows
```
Package Version
------- -------
pip     x.y
```
I use echo to make a file in the magic directory with pytest-watch as its text
```
echo pytest-watch > requirements.txt
```
- echo is a program that writes its given arguments to the standard output (stdout)
- > is an operator that is used to send output from a program to the given file
- pytest-watch is a Python program that automatically runs pytest when a Python file in the folder changes
- pytest is a python package like unittest, that is used for testing
- requirements.txt is the name of a file where I can list python packages for pip to install
  
  Note
  
  requirements.txt is Python convention, I can use any name I want for the file
I install pytest-watch and the programs it needs
```
pip install --requirement requirements.txt
```
- --requirement is another option that can be passed to the install argument for python packages in a given file
- requirements.txt is the name of the file given
  
  Note
  
  requirements.txt is Python convention, I can use any name I want for the file

I use pip to see what packages are now installed in the virtual environment

pip list

the terminal shows

Package      Version
------------ -------
colorama     x.y.z
docopt       x.y.z
iniconfig    x.y.z
packaging    x.y
pip          x.y
pluggy       x.y.z
Pygments     x.y.z
pytest       x.y.z
pytest-watch x.y.z
watchdog     x.y.z

I now have these folders/directories and files in the project

magic
├── .venv
├── src
│   └── magic.py
└── tests
│   ├── __init__.py
│   ├── __pycache__
│   └── test_magic.py
└── requirements.txt

I run the tests from the terminal

pytest-watch

and it shows results without going back to the command line

[TODAYS_DATE] Running: py.test
================== test session starts===================
...
rootdir: .../magic
collected 1 item

tests/test_magic.py .                              [100%]

=============== 1 passed in X.YZs =======================

when I change the input on line 7 in test_magic.py from False to True, the terminal shows AssertionError

====================================== FAILURES =======================================
_______________________________ TestMagic.test_failure ________________________________

self = <tests.test_magic.TestMagic testMethod=test_failure>

    def test_failure(self):
>       self.assertFalse(True)
E       AssertionError: True is not false

tests/test_magic.py:7: AssertionError
============================== short test summary info ================================
FAILED tests/test_magic.py::TestMagic::test_failure - AssertionError: True is not false
================================= 1 failed in X.YZs ===================================

I change True back to False in test_magic.py to make it pass. I can now write the rest of the code for the project while the tests run automatically

Tip

press ctrl + c on the keyboard in the terminal when you want to stop the tests

how to deactivate a virtual environment¶

When I want to leave a virtual environment, I type this in the terminal to deactivate it

deactivate

how to activate a virtual environment¶

When I want to work in a virtual environment, I change directory to the folder/directory that has the virtual environment for example magic, and type this in the terminal

source .venv/bin/activate

the (.venv) on the far left of the command line in the terminal shows that I am in the virtual environment, for example

(.venv) .../magic $

how to automatically make a python test driven development environment¶

You made it this far and have become the greatest programmer in the world. To follow The Do Not Repeat Yourself (DRY) Principle, I write a program that has all the commands it took to get here, then I can use it to make a Test Driven Development Environment anytime I want and not have to remember every step of the process

I exit the tests in the terminal by pressing ctrl + c on the keyboard
I leave the virtual environment
```
deactivate
```
I use cd to change directory to the parent of magic
```
cd ..
```
I use touch to make an empty file with a name that describes what the program does so it is easy to remember later, for example makePythonTdd.sh
```
touch makePythonTdd.sh
```
I use history
```
history
```
the history program shows all the commands I have typed in the terminal so far, and I use them to write the program

I click on makePythonTdd.sh to open it in the Integrated Development Environment (IDE), then type the commands I need to make a Test Driven Development Environment in the editor

Note

the line numbers below are a guide, you do not need to copy them

#!/bin/bash
mkdir magic
cd magic
mkdir src
touch src/magic.py
mkdir tests
touch tests/__init__.py
touch tests/test_magic.py
python3 -m venv .venv
source .venv/bin/activate
python3 -m pip install --upgrade pip
echo pytest-watch > requirements.txt
python3 -m pip install --requirement requirements.txt
pytest-watch

#!/bin/bash is a shebang line that tells the computer to use bash to run the program

The problem with this program is it will always make a project called magic. I need it to be able to make any project I want. I add a variable to replace magic so I can give it any name when I want to make a project

Note

the line numbers below are a guide, you do not need to copy them
```
 1#!/bin/bash
 2PROJECT_NAME=$1
 3mkdir $PROJECT_NAME
 4cd $PROJECT_NAME
 5mkdir src
 6touch src/$PROJECT_NAME.py
 7mkdir tests
 8touch tests/__init__.py
 9touch tests/test_$PROJECT_NAME.py
10python3 -m venv .venv
11source .venv/bin/activate
12python3 -m pip install --upgrade pip
13echo pytest-watch > requirements.txt
14python3 -m pip install --requirement requirements.txt
15pytest-watch
```
$1 is for the first argument given when the program is called, I can use it in place of $PROJECT_NAME for example
```
command argument
```
in the code above, command will be makePythonTdd.sh and $1 will be the value of argument

I use the echo program to add text for the first failing test to test_$PROJECT_NAME.py

#!/bin/bash
PROJECT_NAME=$1
mkdir $PROJECT_NAME
cd $PROJECT_NAME
mkdir src
touch src/$PROJECT_NAME.py
mkdir tests
touch tests/__init__.py

echo "import unittest


class Test$PROJECT_NAME(unittest.TestCase):

    def test_failure(self):
        self.assertFalse(True)


# Exceptions Encountered
# AssertionError
" > tests/test_$PROJECT_NAME.py

python3 -m venv .venv
source .venv/bin/activate
python3 -m pip install --upgrade pip
echo pytest-watch > requirements.txt
python3 -m pip install --requirement requirements.txt
pytest-watch

I type this in the terminal to make sure the program I just wrote can run
```
chmod +x makePythonTdd.sh
```
chmod is a program that changes the mode of the given file

I can make a Test Driven Development environment when I call the program with a name for the PROJECT_NAME variable. For example, when I type this in the terminal in the folder where makePythonTdd.sh is saved

./makePythonTdd.sh calculator

the terminal shows

====================================== FAILURES =======================================
_____________________________ Testcalculator.test_failure _____________________________

self = <tests.test_calculator.Testcalculator testMethod=test_failure>

    def test_failure(self):
>       self.assertFalse(True)
E       AssertionError: True is not false

tests/test_calculator.py:7: AssertionError
=============================== short test summary info ===============================
FAILED tests/test_calculator.py::Testcalculator::test_failure - AssertionError: True is not false
================================== 1 failed in X.YZs ==================================

the computer made a Test Driven Development environment for a project called calculator, you can continue this in how to make a calculator

review¶

One of the advantages of programming is that I can take some steps and make them a one line command for the computer to do for me.

You have seen a way to make a Python Test Driven Development Environment, and have a program to do it for you on any Linux, Windows or MacOS computers.

Would you like to test test AssertionError?

Click Here to see the code for the program to make a Python Test Driven Development environment for any Linux or MacOS computers