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¶

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 it’s 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 to make an empty file
```
touch src/magic.py
```
this adds an empty file for the source code (the actual program)
I make a child 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 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 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 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 having to hit save (ctrl+s) every time I make a change

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
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
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 failures 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

.
------------------------------------------------------
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 it again to see the test pass. I will have to run it again when I make a code change, to make sure tests that were passing are not failing and that the new code I added 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
- .venv is the name given
  
  Note
  
  .venv is Python convention, I can use any name I want
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 python package given
- 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
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

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

The folder/directory structure now looks like this

magic
  ╰──.venv
  ╰──src
  | ╰──magic.py
  ╰──tests
  |  ╰──__pycache__
  |  ╰──__init__.py
  |  ╰──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 to stop the tests at anytime

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 the history program
```
history
```
the terminal shows all the commands I have typed 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 get 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 is executable
```
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 computer will make 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 making a calculator?

makePythonTdd.sh