This is a gist of a pre-commit git hook using raw bash (not https://pre-commit.com/). It must be placed in `.git/hooks/pre-commit`. This gist enters `config` directory with `pyproject.toml` (which has `[mypy]` and `[flake8]` configs). From there it calls both `mypy` and `flake8`. Then it sets up environment variables for `pytest` and calls it.

pre-commit

#!/bin/sh
    ##########################################################################################################
    # I've used this pre-commit hook in my FastAPI app. It launches `bash` session (even on Windows) from the root dir of your project.
    # Meaning if you have a following project structure:
    ###############################
    #   app/                      #
    #       .git                  #
    #       __pycache__           #
    #       .mypy_cache           #
    #       config/               #
    #           pyproject.toml    #
    #       mysite/               #
    #           manage.py         #
    #           mysite/           #
    #               __init__.py   #
    #               settings.py   #
    #               urls.py       #
    #               asgi.py       #
    #               wsgi.py       #
    #       tests/                #
    #           tests_main.py     #
    #           tests_sql.py      #
    ###############################
    # and run:
    # ls -a
    # the output will be '.git, __pycache__, .mypy_cache, config/, mysite/, tests/'.
    # The `bash` session syntax is the same as of normal `bash` in *nix systems.
    # By default this file was named `pre-commit.sample` and the original file can be found at
    # https://github.com/git/git/blob/master/templates/hooks--pre-commit.sample
    # Everything down below is my script.
    ##########################################################################################################
#
# An example hook script to verify what is about to be committed.
# Called by "git commit" with no arguments.  The hook should
# exit with non-zero status after issuing an appropriate message if
# it wants to stop the commit.
#
# To enable this hook, rename this file to "pre-commit".

# Catch changed files
# git diff --cached --name-only --diff-filter=ACMR

cd config

mypy ..
mypy_status=$?
if [ $mypy_status != 0 ]
then
        exit $mypy_status
fi

flake8 ..
flake8_status=$?
if [ $flake8_status != 0 ]
then
        exit $flake8_status
fi

black --check $(git diff --cached --name-only --diff-filter=ACMR)
black_status=$?
if [ $black_status != 0 ]
then
        exit $black_status
fi

cd ..

export DB_USER="user"
export DB_PASSWORD="password"       
export DB_HOST="host"
export DB_PORT="port"
export DB_NAME="name"

export DB_USER_test="user_test"
export DB_PASSWORD_test="password_test"
export DB_HOST_test="host_test"
export DB_PORT_test="port_test"
export DB_NAME_test="name_test"

pytest -v --durations=0 --cache-clear
pytest_status=$?
if [ pytest_status != 0 ]
then
        exit $pytest_status
fi
rm -rf .pytest_cache/

rev. 2
Updated description, because it didn't fit in.

Extra comment:
Exits on mypy/flake8/pytest fails (exit code of any != 0)

rev. 3
Updated description, because it had an error (had tox.ini instead of pyproject.toml.

rev. 4 & 5
Added useful script (5 - fix)

rev. 6
Added example of operation only on changed files

Extra comment:
For more information on --diff-filter check out:
https://git-scm.com/docs/git-diff#Documentation/git-diff.txt---diff-filterACDMRTUXB82308203

rev. 7
Made a more concise example with black.

Extra comment:
I've done this because black is a popular pre-commit hook, which has --check option flag. A user may forget to put this flag so having it in an example is useful.