Testing Python functions running git commands
Let us assume that we would like to implement some Python functions that use the subprocess module to run some git commands. The question is how would you (unit) test such functions?
Sample Python function running a git command
First of all let’s consider the sample Python function below that runs a git command to determine the current git branch.
def current_branch(path: str | Path = '.') -> str | None:
try:
result = subprocess.run(
['git', 'rev-parse', '--abbrev-ref', 'HEAD'],
cwd=path,
capture_output=True,
text=True,
check=True
)
return result.stdout.strip()
except subprocess.CalledProcessError:
return None
How can we test Python functions running git commands?
To test the function above one can write a helper function that initializes a git repo in a temporary test directory and then runs the tests against this directory.
@pytest.fixture
def temp_git_repo(tmp_path: Path) -> Path:
os.chdir(tmp_path)
subprocess.run(['git', 'init'], check=True)
subprocess.run(['git', 'config', 'user.name', 'Test User'], check=True)
subprocess.run(['git', 'config', 'user.email', 'test@example.com'], check=True)
test_file = tmp_path / "test.txt"
test_file.write_text("test content")
subprocess.run(['git', 'add', '.'], check=True)
subprocess.run(['git', 'commit', '-m', 'Initial commit'], check=True)
return tmp_path
def test_current_branch_main(temp_git_repo: Path) -> None:
assert current_branch(temp_git_repo) in ['main', 'master']
Source code is made available on GitHub illustrating the testing approach described in this post.