Why coverage measures test completeness in PyTest - Challenge Your Understanding

Challenge - 5 Problems

🧠 Conceptual

intermediate

Why is code coverage important in testing?

Code coverage helps us understand how much of our code is tested. Why is this important?

A It measures how fast the tests run.

B It guarantees that all bugs are fixed in the code.

C It replaces the need for writing test cases.

D It shows which parts of the code are executed by tests, helping find untested areas.

💡 Hint

Think about what coverage tells you about your tests and code.

Code coverage shows which parts of the code are run during tests. This helps identify untested code, so you can add tests to cover those parts. It does not guarantee bug fixes or test speed.

❓ Predict Output

intermediate

What coverage percentage is shown after running these tests?

Given this simple Python function and tests, what coverage percentage will pytest-cov report?

PyTest

def add(a, b):
    if a > 0:
        return a + b
    else:
        return b


def test_add_positive():
    assert add(2, 3) == 5

# Note: no test for add with a <= 0

A 75% coverage

B 100% coverage

C 50% coverage

D 25% coverage

💡 Hint

Think about which lines run when add(2, 3) is called.

The test calls add with a=2, so the 'if a > 0' branch runs, but the 'else' branch does not. So some lines are not covered, resulting in about 75% coverage.

❓ assertion

advanced

Which assertion best checks test completeness using coverage data?

You have coverage data showing 85% line coverage. Which assertion best verifies your tests cover at least 80% of lines?

A assert coverage_percent == 85

B assert coverage_percent >= 80

C assert coverage_percent < 80

D assert coverage_percent > 85

💡 Hint

Think about verifying minimum coverage threshold.

To check tests cover at least 80%, assert coverage_percent >= 80. Other options check wrong thresholds or exact values.

🔧 Debug

advanced

Why does this coverage report show 0% for a tested function?

Given this code and test, why does coverage show 0% for the function?

PyTest

def multiply(x, y):
    return x * y


def test_multiply():
    result = multiply(3, 4)
    assert result == 12

# Coverage run command: pytest --cov=module_name
# But coverage shows 0% for multiply function

A The module name in the coverage command is incorrect or missing.

B Coverage only measures test execution time, not code run.

C The multiply function has a syntax error.

D The test assertion is wrong, so coverage is zero.

💡 Hint

Check if coverage is pointed to the right code file.

If coverage is run with a wrong or missing module name, it won't measure the function's code, showing 0% coverage even if tests run.

❓ framework

expert

How to configure pytest-cov to fail tests if coverage is below threshold?

Which pytest-cov option configuration will cause tests to fail if coverage is under 90%?

A pytest --cov=module --coverage-fail=90

B pytest --cov=module --fail-under=90

C pytest --cov=module --cov-fail-under=90

D pytest --cov=module --fail-if-coverage-below=90

💡 Hint

Look for the official pytest-cov option to fail on low coverage.

The correct option is --cov-fail-under=90. Other options are invalid and cause errors.