Using pytest to Catch CLI Changes¶

When building CLI apps, it's important to update the major/minor version when the CLI changes (see the semantic versioning philosophy).

How can we ensure we catch these changes with pytest?

syrupy is a great solution.

Let's look at an example for a python CLI that uses typer:

import pytest
import typer
from tpyer.testing import CliRunner
from myapp.cli import app

runner = CliRunner()
commands = list(typer.main.get_group(app).commands.keys())

@pytest.mark.parametrize("cmd", commands)
def test_cli(snapshot, cmd: str):
result = runner.invoke(app, [cmd, "--help"], env={"COLUMNS": "120"})
assert result.exit_code == 0
assert result.stdout == snapshot

Now run pytest --snapshot-update.

This will automatically take whatever you compared snapshot to (in this case result.stdout) and create a copy of that in your tests directory. Now when you run pytest, it compares it to these snapshots.

Whever the CLI changes, it will fail this test until you run pytest --snapshot-update again.