TL;DR: Don't add unnecessary information to your assertions

Problems

• Readability

• Maintainability

Solutions

1. Remove irrelevant data

2. Leave only the needed assertions

Context

Tests should be minimal and follow the SetUp/Exercise/Assert pattern

Sample Code

Wrong

def test_formula_1_race():
    # Setup
    racers = [
        {"name": "Lewis Hamilton", "team": "Mercedes", "starting_position": 1, "car_color": "Silver", "car_model": "W12"},
        {"name": "Max Verstappen", "team": "Red Bull", "starting_position": 2, "car_color": "Red Bull", "car_model": "RB16B"},
        {"name": "Sergio Perez", "team": "Red Bull", "starting_position": 3, "car_color": "Red Bull", "car_model": "RB16B"},
        {"name": "Lando Norris", "team": "McLaren", "starting_position": 4, "car_color": "Papaya Orange", "car_model": "MCL35M"},
        {"name": "Valtteri Bottas", "team": "Mercedes", "starting_position": 5, "car_color": "Silver", "car_model": "W12"},
    ]

    # Exercise
    winner = simulate_formula_1_race(racers)

    # Test
    assert winner == "Lewis Hamilton"

    # This is all irrelevant to the winner asserting
    assert racers[0]["car_color"] == "Silver"
    assert racers[1]["car_color"] == "Red Bull"
    assert racers[2]["car_color"] == "Red Bull"
    assert racers[3]["car_color"] == "Papaya Orange"
    assert racers[4]["car_color"] == "Silver"
    assert racers[0]["car_model"] == "W12"
    assert racers[1]["car_model"] == "RB16B"
    assert racers[2]["car_model"] == "RB16B"
    assert racers[3]["car_model"] == "MCL35M"
    assert racers[4]["car_model"] == "W12"

Right

def test_formula_1_race():
    # Setup
    racers = [
        {"name": "Lewis Hamilton", "starting_position": 1},
        {"name": "Max Verstappen", "starting_position": 2},
        {"name": "Sergio Perez", "starting_position": 3},
        {"name": "Lando Norris", "starting_position": 4},
        {"name": "Valtteri Bottas" "starting_position": 5},
    ]

    # Exercise
    winner = simulate_formula_1_race(racers)

    # Test
    assert winner == "Lewis Hamilton"

Detection

[X] Semi-Automatic

We can find some patterns in not needed assertions.

Tags

• Testing

Conclusion

Tests should be prose. Always focus on the reader. It might be you a couple of months from now.

Relations

More Info

• xUnit Test Patterns: Refactoring Test Code

Disclaimer

Code Smells are my opinion.

Credits

Photo by Evan Demicoli on Unsplash

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Take reasonable steps to test, document, and otherwise draw attention to the assumptions made in every module and routine.

Daniel Read

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This article is part of the CodeSmell Series.