Test-driven development (TDD) concept in Testing Fundamentals - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is the first step in the TDD cycle?

In Test-driven development (TDD), which step comes first in the cycle?

A Write the minimal code to pass the test

B Refactor the existing code to improve structure

C Write a failing test that defines a new function or feature

D Run all tests to ensure everything passes

💡 Hint

Think about what guides the development in TDD.

The TDD cycle starts by writing a test that fails because the feature is not implemented yet. This test defines what the code should do.

❓ Predict Output

intermediate

What is the output of this TDD test run?

Given the following Python test code using unittest, what will be the test result when run the first time?

Testing Fundamentals

import unittest

def add(a, b):
    pass  # Not implemented yet

class TestAdd(unittest.TestCase):
    def test_add_positive(self):
        self.assertEqual(add(2, 3), 5)

if __name__ == '__main__':
    unittest.main()

A Test passes successfully

B Test fails with AssertionError

C SyntaxError due to missing return

D TypeError because add() returns None

💡 Hint

What does the add function return currently?

The add function is not implemented and returns None by default. The test expects 5, so the assertion fails.

❓ assertion

advanced

Which assertion best fits TDD for checking a list contains a new item?

You are writing a test first in TDD to check that a function adds an item to a list. Which assertion is the best choice?

A self.assertIsNotNone(result_list)

B self.assertEqual(result_list[-1], 'item')

C self.assertListEqual(result_list, ['item'])

D self.assertTrue('item' in result_list)

💡 Hint

Focus on what exactly you want to verify about the list.

Using assertTrue with 'in' checks that the item is present anywhere in the list, which is the most direct and flexible check for this case.

🔧 Debug

advanced

Why does this TDD test keep passing incorrectly?

In TDD, you wrote this test and function. The test passes but the function is clearly wrong. Why?

Testing Fundamentals

def is_even(n):
    return True

def test_is_even():
    assert is_even(3) == False
    assert is_even(4) == True

A The test passes because assert statements are not executed when Python runs with optimizations

B The function always returns True, so the test should fail but does not

C The test uses assert statements outside a test framework, so failures are ignored

D The test is not run because it lacks a test framework decorator

💡 Hint

Consider how Python treats assert statements when run with certain flags.

When Python runs with the -O (optimize) flag, assert statements are skipped, so the test does not fail even if the function is wrong.

❓ framework

expert

Which test runner command fits TDD workflow for Python unittest?

In a TDD workflow using Python's unittest, which command runs tests and stops at the first failure to help quick feedback?

A python -m unittest --failfast

B python -m unittest -f

C python -m unittest -v

D python -m unittest discover

💡 Hint

Look for the option that stops testing on first failure.

The --failfast option stops the test run immediately after the first failure, which is useful in TDD for fast feedback.