Python Testing with pytest

Creating Error Conditions

Now let’s check to make sure the Cards CLI deals with error conditions correctly. For example, here’s the delete command implementation:

cards_proj/src/cards/cli.py

@app.command()
def delete(card_id: int):
    """Remove card in db with given id."""
    with cards_db() as db:
        try:
            db.delete_card(card_id)
        except cards.InvalidCardId:
            print(f"Error: Invalid card id {card_id}")

To test the CLI’s handling of an error condition, we can pretend that delete_card generates an exception by assigning the exception to the mock object side_effect attribute, like this:

ch10/test_cli.py

def test_delete_invalid(mock_cardsdb):
    mock_cardsdb.delete_card.side_effect = cards.api.InvalidCardId
 out = cards_cli( ...