how to run tests automatically

In the previous chapters

WSL/Linux/Mac

I ran python3 -m unittest to see the test fail
I ran python3 -m unittest every time I made a change until the test passed

no WSL

I ran python -m unittest to see the test fail
I ran python -m unittest every time I made a change until the test passed

I run that command for each part of the Test Driven Development Cycle or any time there is a code change. I want the computer to automatically run the tests for me so I do not have to keep typing the same command over and over again.

This is one way to automatically run tests in a Python Test Driven Development project. By the end of the chapter you will know these commands better

WSL/Linux/Mac

cd
echo
tree
cat
uv run pytest-watcher
source .venv/bin/activate
deactivate
history

no WSL

cd
Out-File
tree
cat
uv run pytest-watcher
.venv/scripts/activate.ps1
.venv/scripts/activate.bat
deactivate
history

questions about how to run tests automatically

how can I run tests automatically?
how can I stop automated Python tests from running?
what is a Virtual Environment?
how can I activate a Virtual Environment?
how can I deactivate a Virtual Environment?
how can I document the Python programs my project needs?
how can I install the Python programs my project needs from a file?
how can I view all the commands I type in a terminal?

open the project

I change directory to the person folder
```
cd person
```
the terminal shows I am in the person folder
```
.../pumping_python/person
```
I use tree to see what the project looks like, as a reminder
WSL/Linux/Mac
tree -a -L 2
no WSL
tree
I can use pytest-watcher to run tests automatically. It is a Python program that automatically runs pytest any time a Python file changes in the folder it is looking at, this means it will run the tests for me every time I make a change.

pytest is a Python package like unittest that is used for testing. It is not part of The Python Standard Library.

I use uv to run pytest-watcher in the terminal
```
uv run pytest-watcher
```
the terminal is my friend, and shows
```
Using CPython 3.X.Y
Creating virtual environment at: .venv
...
error: Failed to spawn: `pytest-watcher`
  Caused by: No such file or directory (os error 2)
```
- because pytest-watcher is not installed on the computer. I can install pytest-watcher with the uv Python Package Manager.
- the message also shows Creating virtual environment at: .venv
I use tree to see what the project looks like now
WSL/Linux/Mac
tree -a -L 2
no WSL
tree
uv made a virtual environment in a folder named .venv with files and folders.

what is a virtual environment?

A virtual environment is a separate folder where I can install Python packages that my project needs. It helps me keep things that belong to the project in one place, separate from other things on the computer.

I can have a separate virtual environment for every project with only the programs that the project needs. I do not have to keep every program I have ever used for projects that do not need them.

how to write text to a file

I want to make a file where I list all the Python packages that my project needs as a way to document it and have uv install the programs listed in the file

I can write text to a file with the echo program, it shows whatever it is given as an argument, on the screen. For example, if I type this in the terminal
```
echo "Hello, my name is Jacob"
```
it shows
```
Hello, my name is Jacob
```

WSL/Linux/Mac

I can use echo to add text to a file. I use it to make the requirements file with pytest as what is inside it
```
echo "pytest" > requirements.txt
```
> is an operator that is used to send output from a program to the given file

no WSL

I can use Out-File to add text to a file. I use it to make the requirements file with pytest as what is inside it
```
"pytest" | Out-File requirements.txt -Encoding UTF8
```
> is an operator that is used to send output from a program to the given file

pytest is a Python package like unittest, that is used for testing
requirements.txt is the name of the file where I add names of Python packages for the uv Python Package Manager to install. The name requirements.txt is Python convention, I can use any name I want for the requirements file.

I use tree to see what the project looks like now
WSL/Linux/Mac
tree -a -L 1
no WSL
tree
requirements.txt is now in the person folder
I use the cat program to look at what is in requirements.txt
```
cat requirements.txt
```
the terminal shows
```
pytest
```
I add pytest-watcher to the requirements file as well
WSL/Linux/Mac
echo "pytest-watcher" >> requirements.txt
no WSL
"pytest-watcher" >> requirements.txt
- >> is an operator that is used to send output from a program to the given file, it adds to what is in the file without writing over it
- pytest-watcher is a Python program that automatically runs pytest when I change code in the project
I use cat to look at what is in requirements.txt now
```
cat requirements.txt
```
the terminal shows
```
pytest
pytest-watcher
```
life is good!

how to install Python packages with uv

I use cat to show what is in pyproject.toml
```
cat pyproject.toml
```
I use uv to install pytest-watcher from the requirements file
```
uv add --requirement requirements.txt
```
- --requirement is an option that can be given to the add argument for Python packages in a given file
- requirements.txt is the name of the given file. It helps to manage Python programs that are needed by the project. In this case I only have two programs. A project can have a big number of programs it needs and using one file with one command is easier than one command for each program
the terminal is my friend, and shows setup and installation
```
Resolved X packages in GHIms
...
░░░░░░░░░░░░░░░░░░░░ [0/Y] Installing wheels...
...
Installed Z packages in JKLms
 + iniconfig==A.B.C
 + packaging==DE.F
 ~ person==0.1.0 (from file:///.../pumping_python/person)
 + pluggy==G.H.I
 + pygments==J.K.L
 + pytest==M.N.O
 + pytest-watcher==P.Q.R
 + watchdog==S.T.U
```
I run tree to see what changed in the project
WSL/Linux/Mac
tree -a -L 1
no WSL
tree
uv added uv.lock a file that has the exact versions of the Python programs that were installed.
I use cat to show what is now in pyproject.toml
```
cat pyproject.toml
```
it added pytest and pytest-watcher to the dependencies of the project.

how to activate a virtual environment

When I want to work in a virtual environment, I make sure I am in the parent folder of the virtual environment. In this case person is the parent.

WSL/Linux/Mac

I activate the virtual environment in the terminal to use it

source .venv/bin/activate

no WSL

I change the Execution Policy to allow running of scripts

Set-ExecutionPolicy -ExecutionPolicy RemoteSigned -Scope CurrentUser

I activate the virtual environment in the terminal to use it
```
.venv/Scripts/activate.ps1
```
or
```
.venv/Scripts/activate.bat
```

the terminal is my friend, and shows

(person) .../pumping_python/person

(person) on the far left of the command line in the terminal shows that I am working in the virtual environment.

how to deactivate a virtual environment

I can leave the virtual environment by typing deactivate in the terminal

deactivate

the terminal goes back to the command line

.../pumping_python/person

(person) is no longer on the left side.

how to run tests automatically with uv and pytest-watcher

I open test_person.py from the tests folder

I change assert False is False to assert False is True in test_person.py

# False is True
assert False is True
# assert False is False


# Exceptions seen
# AssertionError

I go back to the terminal to run the test again

uv run pytest-watcher . --now

the terminal is my friend, and shows an error without going back to the command line

pytest-watcher version X.Y.Z
Runner command: pytest
Waiting for file changes in .../pumping_python/person
=================== test session starts ====================
platform ____ -- Python 3.A.B, pytest-C.D.E, pluggy-F.G.H
rootdir: .../pumping_python/person
configfile: pyproject.toml
collected 0 items / 1 error

========================== ERRORS ==========================
___________ ERROR collecting tests/test_person.py ___________
tests/test_person.py:2: in <module>
    assert False is True
E   assert False is True
================= short test summary info ==================
ERROR tests/test_person.py - assert False is True
!!!!!!!!!! Interrupted: 1 error during collection !!!!!!!!!!
===================== 1 error in I.JKs =====================
[pytest-watcher]
Current runner args: []
Press w to show menu

better!

how to open the test file in the editor from the terminal

I hold ctrl (Windows/Linux) or option/command (MacOS) on the keyboard, then click on tests/test_person.py to go back to test_person.py. I change True to False

# False is True
# assert False is True
assert False is False


# Exceptions seen
# AssertionError

the terminal shows

[ptw] Detected modified: ./tests/test_person.py ->
=================== test session starts ====================
platform ____ -- Python 3.A.B, pytest-C.D.E, pluggy-F.G.H
rootdir: .../pumping_python/person
configfile: pyproject.toml
collecting ... [ptw] Detected modified: ./tests/test_person.py ->
[ptw] Detected modified: ./tests/test_person.py ->
collected 0 items

================== no tests ran in 0.01s ===================

[pytest-watcher]
Current runner args: []
Press w to show menu

pytest-watcher “saw” the change I made to test_person.py and ran the test .
The terminal shows no tests ran which is confusing since the only way I know the test passed, is because I saw it fail.

I can write the rest of the code for the project and get results back quickly because the tests run when I change the code.

I want to write code that represents a person, after I learn what an assertion is.

how to stop the automated tests

I go to the terminal and use q on the keyboard to stop the tests, the terminal goes back to the command line.

.../pumping_python/person

close the project

I click in the terminal then add the new files and folders to git for tracking
```
git add .
```
the terminal goes back to the command line.
I add a git commit message
```
git commit --all --message \
'automate tests'
```
the terminal shows a summary of the changes then goes back to the command line.
I close test_person.py
I change directory to the parent of person
```
cd ..
```
.. is for the parent of any directory I am in. the terminal shows
```
.../pumping_python
```
I am back in the pumping_python folder.

review

I gave the computer some commands to automate running tests for my Python Test Driven Development environment
I used uv to make a virtual environment
I made a requirements file_ for my project dependencies
I installed pytest-watcher from the requirements file
I ran the test automatically with uv and pytest-watcher

how to view all the commands I typed to automate running tests

I type history in the terminal to see all the commands I typed in this chapter

history

the terminal shows

WSL/Linux/Mac

cd person
tree -a -L 2
uv run pytest-watcher
tree -a -L 2
echo "Hello, my name is Jacob"
echo "pytest" > requirements.txt
tree -a -L 1
cat requirements.txt
echo "pytest-watcher" >> requirements.txt
cat requirements.txt
cat pyproject.toml
uv add --requirement requirements.txt
tree -a -L 1
cat pyproject.toml
source .venv/bin/activate
deactivate
uv run pytest-watcher . --now
git add .
git commit --all --message 'automate tests'
cd ..

no WSL

cd person
tree
uv run pytest-watcher
tree
echo "Hello, my name is Jacob"
"pytest" | Out-File requirements.txt -Encoding UTF8
tree
cat requirements.txt
"pytest-watcher" >> requirements.txt
cat requirements.txt
cat pyproject.toml
uv add --requirement requirements.txt
tree
cat pyproject.toml
Set-ExecutionPolicy -ExecutionPolicy RemoteSigned -Scope CurrentUser
.venv/Scripts/activate.ps1
deactivate
uv run pytest-watcher . --now
git add .
git commit --all --message 'automate tests'
cd ..

the history program shows all the commands I typed in the terminal.

these are the commands I used to make a Python Test Driven Development environment then run the tests automatically

WSL/Linux/Mac

uv init NAME_OF_THE_PROJECT
cd NAME_OF_THE_PROJECT
mkdir tests
touch tests/__init__.py
touch tests/test_NAME_OF_THE_PROJECT.py
echo "pytest" > requirements.txt
echo "pytest-watcher" >> requirements.txt
uv add --requirement requirements.txt
uv run pytest-watcher . --now

no WSL

uv init NAME_OF_THE_PROJECT
cd NAME_OF_THE_PROJECT
mkdir tests
touch tests/__init__.py
touch tests/test_NAME_OF_THE_PROJECT.py
"pytest" | Out-File requirements.txt
"pytest-watcher" >> requirements.txt
uv add --requirement requirements.txt
uv run pytest-watcher . --now

where NAME_OF_THE_PROJECT is the name I give the project.

these are the steps I took to make a Python Test Driven Development environment then run the tests automatically

How many questions can you answer after going through this chapter?

what is next?

Would you like to know what causes AssertionError

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