Quiz: Testing and Debugging

Test your understanding before moving on. Target: 70% or higher to proceed confidently.

Section 1: Multiple Choice (1 point each)

1. What is a unit test?

• A) A test that checks the entire program end-to-end
• B) A test that checks a single, small piece of code in isolation
• C) A test that checks how multiple modules work together
• D) A test that measures how fast your code runs

2. Which pytest naming convention is REQUIRED for test discovery?

• A) Test files must end with .py and test functions must contain the word "test"
• B) Test files must start with test_ (or end with _test.py) and test functions must start with test_
• C) Test files and functions can be named anything as long as they contain assertions
• D) Test files must be in a directory called tests/

3. What does the following test verify?

def test_empty_list():
    with pytest.raises(ValueError):
        calculate_average([])

• A) That calculate_average returns ValueError when given an empty list
• B) That calculate_average raises a ValueError exception when given an empty list
• C) That calculate_average returns an empty list
• D) That calculate_average handles empty lists without crashing

4. In test-driven development, what is the correct order of the three steps?

• A) Green, Red, Refactor
• B) Refactor, Red, Green
• C) Red, Green, Refactor
• D) Red, Refactor, Green

5. Why is it important that a new test FAILS before you write the implementation?

• A) Because failing tests run faster
• B) Because it proves the test is actually checking something meaningful
• C) Because pytest requires at least one failure per session
• D) Because it helps you memorize the error messages

6. Which of the following is an edge case for a function that finds the maximum value in a list?

• A) A list of 10 random positive integers
• B) A list with a single element
• C) A list of numbers in ascending order
• D) A list of numbers where the max is in the middle

7. What is a pytest fixture?

• A) A special assertion that checks multiple conditions at once
• B) A function decorated with @pytest.fixture that provides shared test data or setup
• C) A configuration file that tells pytest where to find tests
• D) A plugin that adds extra assertion methods

8. What debugging strategy involves checking the midpoint of your code first, then narrowing down which half contains the bug?

• A) Rubber duck debugging
• B) Print debugging
• C) Binary search debugging
• D) Breakpoint debugging

9. Why is this function HARD to test?

def get_user_age():
    age = int(input("Enter your age: "))
    if age >= 18:
        print("You are an adult.")
    else:
        print("You are a minor.")

• A) Because it uses int() which can crash
• B) Because it uses input() and print() instead of parameters and return values
• C) Because it doesn't have a docstring
• D) Because it doesn't handle negative ages

10. What does code coverage measure?

• A) How many bugs your tests have found
• B) What percentage of your code is executed by your test suite
• C) How many test functions you've written
• D) How fast your tests run

Section 2: Short Answer (2 points each)

11. Explain why 100% code coverage does not guarantee that your code is correct. Give a specific example.

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

def test_add():
    add(2, 3)  # Executes add() but never checks the result

12. What is the difference between a regression test and a unit test?

13. Describe the "separate logic from I/O" principle. How would you refactor a function that both reads user input and performs a calculation?

14. Write three boundary condition tests for a function is_passing(score) that returns True if score >= 60 and False otherwise. Explain why each test is important.

def test_exactly_at_boundary():
    assert is_passing(60) is True  # The exact cutoff — often where off-by-one bugs hide

def test_just_below_boundary():
    assert is_passing(59) is False  # One below the cutoff — catches >= vs > errors

def test_just_above_boundary():
    assert is_passing(61) is True  # One above — confirms the boundary isn't shifted

Section 3: Code Analysis (3 points each)

15. Read the following code and predict exactly what pytest will output (pass/fail for each test, and what error if any):

def multiply(a, b):
    return a * b

def test_multiply_integers():
    assert multiply(3, 4) == 12

def test_multiply_by_zero():
    assert multiply(5, 0) == 0

def test_multiply_strings():
    assert multiply("ha", 3) == "hahaha"

def test_multiply_negative():
    assert multiply(-2, 3) == 6

16. This fixture has a subtle problem. What is it, and how would you fix it?

@pytest.fixture
def shared_list():
    return [1, 2, 3]

def test_append(shared_list):
    shared_list.append(4)
    assert len(shared_list) == 4

def test_length(shared_list):
    assert len(shared_list) == 3

17. Identify all the problems with this test suite:

def test_everything():
    # Test addition
    assert 2 + 3 == 5
    # Test string upper
    assert "hello".upper() == "HELLO"
    # Test list append
    data = [1, 2]
    data.append(3)
    assert len(data) == 3
    # Test dictionary
    d = {"a": 1}
    assert d["a"] == 1

Section 4: Applied Problem (4 points)

18. Write a complete test suite (at least 6 tests) for this function. Include normal cases, edge cases, and error cases:

def find_longest_word(sentence):
    """Return the longest word in a sentence. If there's a tie, return the first one."""
    if not sentence or not sentence.strip():
        raise ValueError("Sentence cannot be empty")
    words = sentence.split()
    longest = words[0]
    for word in words[1:]:
        if len(word) > len(longest):
            longest = word
    return longest

import pytest

def test_single_word():
    assert find_longest_word("hello") == "hello"

def test_multiple_words():
    assert find_longest_word("the quick fox") == "quick"

def test_tie_returns_first():
    assert find_longest_word("cat dog rat") == "cat"  # All length 3, return first

def test_longest_at_end():
    assert find_longest_word("a bb ccc") == "ccc"

def test_longest_at_start():
    assert find_longest_word("elephant is big") == "elephant"

def test_empty_string_raises():
    with pytest.raises(ValueError):
        find_longest_word("")

def test_whitespace_only_raises():
    with pytest.raises(ValueError):
        find_longest_word("   ")

def test_extra_whitespace():
    assert find_longest_word("  hello   world  ") == "hello"

19. You have a function parse_date(date_string) that converts strings like "2025-03-15" into a dictionary {"year": 2025, "month": 3, "day": 15}. Using TDD, show the Red-Green-Refactor process: write your first three tests, then write the implementation. Show each step.

def test_parse_standard_date():
    assert parse_date("2025-03-15") == {"year": 2025, "month": 3, "day": 15}

def test_parse_january_first():
    assert parse_date("2024-01-01") == {"year": 2024, "month": 1, "day": 1}

def test_parse_invalid_format_raises():
    with pytest.raises(ValueError):
        parse_date("March 15, 2025")

def parse_date(date_string):
    parts = date_string.split("-")
    if len(parts) != 3:
        raise ValueError(f"Invalid date format: {date_string}")
    try:
        return {
            "year": int(parts[0]),
            "month": int(parts[1]),
            "day": int(parts[2])
        }
    except ValueError:
        raise ValueError(f"Invalid date format: {date_string}")

20. Read the following buggy function and, without running it, predict what process_scores([85, 92, 78, 90, 88]) returns. Then identify the bug and fix it.

def process_scores(scores):
    """Return a dict with min, max, and average of the scores,
    excluding the lowest score."""
    sorted_scores = sorted(scores)
    trimmed = sorted_scores[1:]  # Remove lowest
    return {
        "min": min(scores),
        "max": max(scores),
        "average": sum(trimmed) / len(trimmed)
    }

def process_scores(scores):
    sorted_scores = sorted(scores)
    trimmed = sorted_scores[1:]
    return {
        "min": min(trimmed),
        "max": max(trimmed),
        "average": sum(trimmed) / len(trimmed)
    }