Node.js built-in test runner in Node.js - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the Node.js built-in test runner?

It is a simple testing tool included with Node.js that lets you write and run tests without installing extra packages.

beginner

How do you run tests using the Node.js built-in test runner?

Use the command node --test in your terminal to run test files automatically detected by Node.js.

beginner

Which module do you import to write tests with Node.js built-in test runner?

You import the <code>test</code> function from the <code>node:test</code> module to define your tests.

beginner

What is the purpose of assertions in Node.js built-in test runner?

Assertions check if your code behaves as expected. If an assertion fails, the test fails and shows an error.

intermediate

How do you write an asynchronous test using Node.js built-in test runner?

You define the test function as async and use await inside it. The test runner waits for the async code to finish.

Which command runs tests using the Node.js built-in test runner?

A node test.js

B node --test

C npm test

D npm run test

The correct command is node --test which runs tests using the built-in test runner.

Which module provides the test function in Node.js built-in test runner?

A node:test

B assert

C mocha

D jest

The node:test module provides the test function for writing tests.

What happens if an assertion fails in a Node.js built-in test runner test?

A The test runner crashes

B The test passes anyway

C The test fails and shows an error

D Nothing happens

If an assertion fails, the test fails and the error is reported.

How do you write an asynchronous test with Node.js built-in test runner?

A Define the test function as async and use await inside

B Use callbacks only

C Use setTimeout to delay assertions

D Asynchronous tests are not supported

You write async tests by marking the test function async and using await inside it.

Which of these is NOT a feature of Node.js built-in test runner?

A Runs tests without extra packages

B Supports test grouping and hooks

C Automatically detects test files

D Provides a graphical user interface

The built-in test runner does not have a graphical user interface; it runs tests in the terminal.

Explain how to write and run a simple test using the Node.js built-in test runner.

Think about the steps from writing code to running it in terminal.

Describe how asynchronous code is tested using the Node.js built-in test runner.

Consider how async/await works in JavaScript tests.

Practice

1. What is the main purpose of the Node.js built-in test runner?

easy

A. To write and run tests easily without extra tools

B. To compile Node.js code faster

C. To deploy Node.js applications automatically

D. To monitor server performance in real-time

Solution

1. Step 1: Understand the role of the test runner

   The Node.js built-in test runner is designed to help developers write and run tests without needing additional testing frameworks.

2. Step 2: Compare options with this purpose

   Options B, C, and D describe unrelated tasks like compiling, deploying, or monitoring, which are not the test runner's function.

3. Final Answer:

   To write and run tests easily without extra tools -> Option A

4. Quick Check:

   Test runner purpose = write and run tests [OK]

Hint: Test runner = tool to run tests simply [OK]

Common Mistakes:

• Confusing test runner with build tools
• Thinking it deploys apps
• Assuming it monitors performance

2. Which of the following is the correct way to import the assertion module in a Node.js test file?

easy

A. const assert = require('assert');

B. import assert from 'assert';

C. import { assert } from 'assert';

D. require import assert from 'assert';

Solution

1. Step 1: Recall Node.js import syntax for CommonJS

   Node.js traditionally uses const assert = require('assert'); to import modules in CommonJS style.

2. Step 2: Check each option's syntax

   import assert from 'assert'; uses ES module syntax but without enabling ES modules, it may fail. import { assert } from 'assert'; is incorrect because assert is the default export, not a named export. require import assert from 'assert'; is invalid syntax.

3. Final Answer:

   const assert = require('assert'); -> Option A

4. Quick Check:

   CommonJS import = require() [OK]

Hint: Use require() for assert in Node.js tests [OK]

Common Mistakes:

• Using ES module import without config
• Trying to destructure assert
• Mixing require and import keywords

3. What will be the output when running the following test code with node --test?

import test from 'node:test';
import assert from 'assert';

test('simple addition', () => {
  assert.strictEqual(2 + 2, 4);
});

test('failing test', () => {
  assert.strictEqual(3 * 3, 8);
});

medium

A. Both tests fail with assertion errors

B. Both tests pass with no errors

C. Syntax error stops tests from running

D. First test passes, second test fails with assertion error

Solution

1. Step 1: Analyze each test assertion

   The first test checks if 2 + 2 equals 4, which is true, so it passes. The second test checks if 3 * 3 equals 8, which is false, so it fails.

2. Step 2: Understand test runner behavior

   Node.js test runner runs all tests and reports which pass or fail. It does not stop on first failure.

3. Final Answer:

   First test passes, second test fails with assertion error -> Option D

4. Quick Check:

   Correct assertions pass, wrong ones fail [OK]

Hint: Check each assertion result carefully [OK]

Common Mistakes:

• Assuming all tests pass
• Thinking syntax error occurs
• Believing test runner stops on first fail

4. Identify the error in this test code snippet:

import test from 'node:test';
import assert from 'assert';

test('check truth', () => {
  assert.equal(true, 1);
});

medium

A. Test name must be a function, not a string

B. Using assert.equal instead of assert.strictEqual causes a type coercion issue

C. Incorrect import statement for test module

D. Missing async keyword in test callback

Solution

1. Step 1: Understand assert.equal vs assert.strictEqual

   assert.equal uses loose equality (==) which allows type coercion, so true == 1 passes, but this can cause unexpected results.

2. Step 2: Identify best practice for strict checks

   Using assert.strictEqual is recommended to avoid type coercion and ensure exact equality.

3. Final Answer:

   Using assert.equal instead of assert.strictEqual causes a type coercion issue -> Option B

4. Quick Check:

   Use strictEqual to avoid type coercion [OK]

Hint: Prefer strictEqual for exact matches [OK]

Common Mistakes:

• Ignoring difference between equal and strictEqual
• Thinking async is always required
• Misunderstanding import syntax

5. You want to write a test that checks if a function getUserName(id) returns a non-empty string for valid IDs and throws an error for invalid IDs. Which approach correctly uses the Node.js built-in test runner and assertions?

hard

A. Use assert.strictEqual(getUserName(validId), '') and no error test

B. Use one test with assert.equal(getUserName(validId), 'non-empty') and ignore errors

C. Use two tests: one with assert.ok(typeof result === 'string' && result.length > 0), another with assert.throws(() => getUserName(invalidId))

D. Use console.log to check outputs manually instead of assertions

Solution

1. Step 1: Define tests for both valid and invalid cases

   Testing valid IDs requires checking the return is a non-empty string. Testing invalid IDs requires checking that an error is thrown.

2. Step 2: Use appropriate assertions

   assert.ok can check conditions like type and length. assert.throws verifies that calling the function with invalid input throws an error.

3. Final Answer:

   Use two tests: one with assert.ok(typeof result === 'string' && result.length > 0), another with assert.throws(() => getUserName(invalidId)) -> Option C

4. Quick Check:

   Separate tests for success and error cases [OK]

Hint: Test success and error cases separately with assert [OK]

Common Mistakes:

• Ignoring error case tests
• Checking empty string instead of non-empty
• Using console.log instead of assertions