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Testing & modern typing

pytest basics, mocks, type hints, TypedDict, Protocol, and static-checking patterns.

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Testing & modern typing easy

How to Mock subprocess.run returncode in Python

Simulate subprocess.run return codes in tests with unittest.mock.patch and CompletedProcess.

unittest mock subprocess
Python 
import subprocess
from unittest.mock import patch


def run_command(cmd):
    result = subprocess.run(cmd, capture_output=True, text=True)
    return result.returncode


if __name__ == "__main__":
    with patch("subprocess.run") as mock_run:
        # Simulate a successful command (returncode 0)
        mock_run.retu…
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