Version control and testing: Exercise/discussion: Testing using hooks

Git hooks

Git hooks are scripts that we can define and which can be run when certain Git events happen. They can, for example, run tests before a commit and reject if it fails.

There are client-side hooks (run on your own computer when committing) and server-side hooks (run on server after pushing, usually used to test if merging is okay).

Type-along: Testing using a pre-commit hook

Here we will use our previous example.py and add a git client-side hook the pre-commit hook to run a script before a commit is recorded.

1. The starting point is our example.py file

We are still in the directory pytest-example which contains example.py:

def add(a, b):
    return a + b


def test_add():
    assert add(2, 3) == 5
    assert add('space', 'ship') == 'spaceship'

2. Make sure the test passes

$ pytest example.py

3. Initialize a Git repository

$ git init

4. Git add and commit the file

$ git add example.py
$ git commit

5. Create the following shell script

Save this file as pre-commit:

#!/bin/bash

pytest example.py

6. Make pre-commit executable

$ chmod +x pre-commit

7. Move this file under .git/hooks

$ mv pre-commit .git/hooks

8. Break the code and try to commit this change

Now the pre-commit should reject the commit.

9. Discuss

Discuss this approach: pros and cons.