ACS 3310 — Lab 3: Writing Unit Tests

Overview

In this lab you will practice writing unit tests for existing code.

You will NOT be writing new functions from scratch. Instead, your goal is to:

• understand what each function is supposed to do
• write tests that describe correct behavior
• use tests to detect bugs
• fix any bugs you discover

This lab builds directly on Lesson 3:

Tests are used to prove behavior, not just check it.

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What You Are Solving

You are given a set of functions in:

src/functions.ts

Some of these functions are incorrect.

Your job is to:

1. Write tests that describe what each function should do
2. Use those tests to reveal incorrect behavior
3. Fix the implementation so all tests pass

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Learning Goals

By the end of this lab you should be able to:

• write unit tests using Vitest
• describe expected behavior using expect
• identify edge cases
• use tests to reveal and fix bugs

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Setup

Clone your repository:

git clone <your-repo-url>
cd ACS-3310-Lab-3

Install dependencies:

npm install

Run the tests:

npm test

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Your Task

For each function in src/functions.ts:

• write at least 2 meaningful tests
• include at least 1 edge case
• make sure your tests clearly describe expected behavior

Your tests should:

• FAIL when the function behaves incorrectly
• PASS after the function is fixed

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Important: Tests Should Fail First

When you begin this lab, all tests will pass because no real tests have been written.

As you write tests, you should expect:

• some tests to FAIL at first
• failures mean your tests are working
• failures reveal bugs in the code

If your tests never fail, they are not useful.

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What You Will Edit

You should primarily edit:

tests/functions.test.ts

You may also edit:

src/functions.ts

…but only after your tests reveal incorrect behavior.

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What Is an Edge Case?

An edge case is a boundary or unusual input where bugs often occur.

Examples:

• empty arrays
• single-item arrays
• very small or large values

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Definition of Done

You are finished when:

• you have written meaningful tests for each function
• your tests FAIL for incorrect behavior (at least initially)
• you fix the implementation
• all tests PASS (npm test)
• your code is pushed to GitHub

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Tips

• Start by writing tests before changing any code
• Read each function carefully
• Ask: What should this do?
• Use failing tests to guide your fixes
• Avoid weak or duplicate tests

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Submission

Your work is submitted automatically when you push to GitHub.

git add .
git commit -m "complete lab 3"
git push

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Reminder

You are not just fixing bugs.

You are writing tests that prove the bugs exist, then verifying that your fixes work.