Single responsibility per test in PyTest - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Why keep one assertion per test?

Why is it best to have only one assertion in a test function?

A It makes it easier to find the exact cause when a test fails.

B It reduces the total number of tests needed.

C It allows multiple features to be tested together efficiently.

D It speeds up test execution by combining checks.

💡 Hint

Think about how you find problems quickly when something breaks.

Having one assertion per test helps quickly identify what exactly failed. If multiple assertions are in one test, you might not know which part caused the failure without extra debugging.

❓ Predict Output

intermediate

Output of pytest with multiple assertions

What will pytest report when running this test?

PyTest

def test_numbers():
    assert 2 + 2 == 4
    assert 3 * 3 == 10
    assert 5 - 2 == 3

A Test fails at first assertion with AssertionError.

B Test passes because only one assertion needs to be true.

C Test fails at second assertion with AssertionError.

D Test fails at third assertion with AssertionError.

💡 Hint

Remember pytest stops at the first failed assertion in a test.

The first assertion passes, but the second assertion (3 * 3 == 10) is false, so pytest stops and reports failure there.

❓ assertion

advanced

Choose the best single responsibility test assertion

Which assertion best follows the single responsibility principle for testing a function is_even(n) that returns True if n is even?

PyTest

def is_even(n):
    return n % 2 == 0

A assert is_even(2) is True

B assert is_even(2) is True and is_even(3) is False

C assert is_even(3) is False

D assert is_even(2) == True or is_even(3) == False

💡 Hint

Focus on testing one behavior per test.

Option A tests only one case (2 is even), keeping the test focused. Option A tests two cases in one assertion, which breaks single responsibility. Option A tests a different case and should be a separate test. Option A uses 'or' which can hide failures.

🔧 Debug

advanced

Identify the problem with this test function

What is the main issue with this pytest test function?

PyTest

def test_user_profile():
    assert user.name == 'Alice'
    assert user.age == 30
    assert user.email == '[e-mail]'

A The test has multiple assertions, making it hard to know which failed.

B The assertions use wrong syntax for equality check.

C The test function name does not start with 'test_'.

D The test is missing a setup for the user object.

💡 Hint

Check if all variables used are defined or initialized.

The test uses 'user' without defining or initializing it, so it will raise a NameError before assertions run. Multiple assertions are allowed but setup is required.

❓ framework

expert

Best pytest structure for single responsibility tests

Which pytest structure best supports single responsibility per test for a function add(a, b)?

PyTest

def add(a, b):
    return a + b

A One test function with multiple assertions for all input cases.

B Separate test functions each with one assertion for different input cases.

C One test function with a loop and assertions inside for all cases.

D One test function that asserts the output type only.

💡 Hint

Think about clarity and easy failure detection.

Separate test functions with one assertion each make it clear which input case fails. Multiple assertions or loops in one test hide which case caused failure. Testing only output type is insufficient.