Python Testing with pytest

Using capsys

Sometimes the application code is supposed to output something to stdout, stderr, and so on. As it happens, the Cards sample project has a command-line interface that should be tested.

The command, cards version, is supposed to output the version:

$ cards version
1.0.0

The version is also available from the API:

$ python -i
>>> import cards
>>> cards.__version__
'1.0.0'

One way to test this would be to actually run the command with subprocess.run(), grab the output, and compare it to the version from the API:

ch4/test_version.py

import subprocess


def test_version_v1():
    process = subprocess.run(
        ["cards", "version"], capture_output=True, text=True
    )
 output = process.stdout.rstrip() ...