Unit testing in Testing Fundamentals - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is unit testing?

Unit testing is the process of testing small parts of a program, called units, to make sure each part works correctly on its own.

beginner

Why do we write unit tests?

We write unit tests to catch mistakes early, make fixing bugs easier, and help keep code working well when we change it later.

beginner

What is a test case in unit testing?

A test case is a set of instructions that checks if a small part of the program behaves as expected with certain inputs.

beginner

What does it mean if a unit test fails?

If a unit test fails, it means the part of the program tested did not work as expected and needs fixing.

beginner

Name one benefit of automated unit testing.

Automated unit testing saves time by running tests quickly and often without needing a person to do it each time.

What does a unit test check?

A Network connectivity

B The entire software system

C User interface design

D A small part of the program

Unit tests focus on small parts, or units, of the program to verify they work correctly.

When should unit tests be run?

A Often during development

B Before writing any code

C Only when bugs appear

D Only after the whole project is finished

Running unit tests often during development helps catch problems early.

What is a test case in unit testing?

A A bug report

B A set of instructions to check code behavior

C A user manual

D A software requirement

A test case defines inputs and expected results to check if code works as intended.

If a unit test fails, what should you do?

A Delete the test

B Ignore it

C Fix the code or test

D Restart the computer

A failing test means something is wrong and needs fixing.

Which is a benefit of automated unit tests?

A They can run tests quickly and repeatedly

B They require no maintenance

C They run slower than manual tests

D They replace the need for developers

Automated tests save time by running tests fast and often without manual effort.

Explain what unit testing is and why it is important.

Think about testing one small piece of a program at a time.

Describe what a test case is and what it should include.

A test case is like a recipe for checking if code works.

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