Unit testing in Testing Fundamentals - Build an Automation Script

Unit test for a simple calculator add function

Preconditions (1)

Step 1: Call add(2, 3)

Step 2: Call add(-1, 5)

Step 3: Call add(0, 0)

✅ Expected Result: The add function returns 5, 4, and 0 respectively for the calls

Automation Requirements - unittest

Assertions Needed:

assertEqual for checking returned sum

Best Practices:

Use setUp method if needed for initialization

Test one behavior per test method

Name test methods clearly

Keep tests independent

Automated Solution

Testing Fundamentals

import unittest

# Simple calculator module
class Calculator:
    @staticmethod
    def add(a, b):
        return a + b

class TestCalculator(unittest.TestCase):
    def test_add_positive_numbers(self):
        result = Calculator.add(2, 3)
        self.assertEqual(result, 5)

    def test_add_negative_and_positive(self):
        result = Calculator.add(-1, 5)
        self.assertEqual(result, 4)

    def test_add_zeros(self):
        result = Calculator.add(0, 0)
        self.assertEqual(result, 0)

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

This code defines a simple Calculator class with a static add method.

The TestCalculator class inherits from unittest.TestCase and contains three test methods.

Each test calls the add method with specific inputs and uses assertEqual to check the output matches the expected sum.

Tests are independent and clearly named to show what they check.

Running this script will execute all tests and report pass/fail results.

Common Mistakes - 4 Pitfalls

Not using assertEqual and instead printing results

Testing multiple behaviors in one test method

{'mistake': "Not naming test methods starting with 'test_'", 'why_bad': 'unittest framework will not recognize methods as tests without this prefix.', 'correct_approach': "Always start test method names with 'test_'."}

Relying on external state or previous tests

Bonus Challenge

Now add data-driven testing with 3 different input pairs for the add function

Show Hint

Practice

1. What is the main purpose of unit testing in software development?

easy

A. To deploy the software to users

B. To test the entire software system at once

C. To check small parts of code work correctly

D. To design the user interface

Solution

1. Step 1: Understand unit testing scope

   Unit testing focuses on testing small, individual parts of code, like functions or methods.

2. Step 2: Compare with other testing types

   Testing the entire system is integration or system testing, not unit testing.

3. Final Answer:

   To check small parts of code work correctly -> Option C

4. Quick Check:

   Unit testing = small code parts check [OK]

Hint: Unit tests check small code parts, not whole system [OK]

Common Mistakes:

• Confusing unit testing with system testing
• Thinking unit tests check UI or deployment
• Believing unit tests run the full application

2. Which of the following is the correct syntax for a simple unit test assertion in Python using assert?

easy

A. assert add(2, 3) == 5

B. assert add(2, 3) = 5

C. assert(add(2, 3) = 5)

D. assert add(2, 3) equals 5

Solution

1. Step 1: Recall Python assert syntax

   Python uses assert expression where expression must be True for test to pass.

2. Step 2: Check each option

   assert add(2, 3) == 5 uses correct syntax: assert add(2, 3) == 5. assert add(2, 3) = 5 uses single = which is assignment, invalid here. assert(add(2, 3) = 5) uses single = which is assignment, invalid syntax. assert add(2, 3) equals 5 uses invalid keyword 'equals'.

3. Final Answer:

   assert add(2, 3) == 5 -> Option A

4. Quick Check:

   assert with == for comparison [OK]

Hint: Use 'assert expression' with '==' for comparison in Python [OK]

Common Mistakes:

• Using single '=' instead of '==' in assert
• Writing assert with invalid keywords
• Adding unnecessary parentheses in assert

3. Given the Python function and test below, what will be the test result?

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

assert multiply(3, 4) == 12
assert multiply(0, 5) == 0
assert multiply(-1, 3) == -3
assert multiply(2, 2) == 5

medium

A. The last assertion fails

B. All assertions pass

C. The first assertion fails

D. The second assertion fails

Solution

1. Step 1: Evaluate each assertion

   multiply(3,4) = 12 matches expected 12 (pass). multiply(0,5) = 0 matches 0 (pass). multiply(-1,3) = -3 matches -3 (pass). multiply(2,2) = 4 but expected 5 (fail).

2. Step 2: Identify failing assertion

   The last assertion expects 5 but function returns 4, so it fails.

3. Final Answer:

   The last assertion fails -> Option A

4. Quick Check:

   4 != 5 causes failure [OK]

Hint: Check each assert expected vs actual carefully [OK]

Common Mistakes:

• Assuming all assertions pass without checking values
• Confusing multiplication results
• Ignoring the last assertion

4. Identify the error in the following Python unit test code:

def divide(a, b):
    return a / b

assert divide(10, 2) == 5
assert divide(5, 0) == 0

medium

A. The function should return integer only

B. Division by zero causes runtime error

C. The first assertion is incorrect

D. Assertions are missing parentheses

Solution

1. Step 1: Analyze function behavior

   Function divides a by b. Dividing by zero is not allowed and causes an error.

2. Step 2: Check assertions

   First assertion divides 10 by 2, which is valid. Second assertion divides 5 by 0, which causes a runtime ZeroDivisionError.

3. Final Answer:

   Division by zero causes runtime error -> Option B

4. Quick Check:

   Divide by zero error in second assert [OK]

Hint: Watch for zero division in tests [OK]

Common Mistakes:

• Ignoring division by zero error
• Thinking assertions need parentheses in Python
• Assuming function returns only integers

5. You want to write a unit test for a function that returns the maximum number from a list. Which test case below best checks the function handles an empty list correctly?

hard

A. assert max_number([-1, -2]) == -1

B. assert max_number([1, 2, 3]) == 3

C. assert max_number([0]) == 0

D. assert max_number([]) == None

Solution

1. Step 1: Understand the edge case

   An empty list has no maximum value, so the function should handle this gracefully, often by returning None or raising an error.

2. Step 2: Evaluate test cases

   assert max_number([]) == None tests the empty list case expecting None, which is appropriate. Other options test normal lists, not empty.

3. Final Answer:

   assert max_number([]) == None -> Option D

4. Quick Check:

   Empty list test expects None [OK]

Hint: Test empty inputs with None or error expected [OK]

Common Mistakes:

• Not testing empty list edge case
• Using normal list tests for empty case
• Assuming empty list returns zero