Node.js built-in test runner in Node.js - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple Node.js test

What is the output when running this Node.js test code using the built-in test runner?

Node.js

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

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

A RuntimeError because 'assert' module is not imported.

B Test fails with an AssertionError because 2 + 2 is not equal to 4.

C Test passes with no output except a summary line indicating 1 test passed.

D SyntaxError due to missing parentheses in the test function.

💡 Hint

Check what assert.strictEqual does when the values are equal.

The test checks if 2 + 2 equals 4, which is true, so the assertion passes and the test runner reports success.

❓ assertion

intermediate

Choosing the correct assertion for error testing

Which assertion correctly tests that a function throws an error using Node.js built-in test runner?

Node.js

function willThrow() {
  throw new Error('fail');
}

A assert.equal(willThrow(), 'fail');

B assert.doesNotThrow(() => willThrow());

C assert.strictEqual(willThrow(), Error);

D assert.throws(() => willThrow(), Error);

💡 Hint

Use the assertion that expects a function to throw an error.

assert.throws expects a function that throws an error; it passes if the error is thrown.

🔧 Debug

advanced

Debugging a failing test with async code

This test is supposed to check if an async function returns 'done', but it fails. What is the cause?

Node.js

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

async function asyncFunc() {
  return 'done';
}

test('async test', () => {
  const result = asyncFunc();
  assert.strictEqual(result, 'done');
});

A assert.strictEqual cannot compare strings.

B The test does not await the async function, so result is a Promise, not 'done'.

C The async function throws an error that is not caught.

D The test function must be named differently to support async.

💡 Hint

Remember what async functions return.

asyncFunc returns a Promise; without await, result is a Promise, so assertion fails.

❓ framework

advanced

Understanding test hooks in Node.js built-in test runner

Which hook runs once before all tests in a file when using Node.js built-in test runner?

A test.beforeAll()

B test.beforeEach()

C test.setup()

D test.before()

💡 Hint

Look for the hook that runs once before all tests.

test.beforeAll() runs once before all tests; test.beforeEach() runs before each test.

🧠 Conceptual

expert

Test report output for multiple tests with failures

Given this test file with two tests, one passing and one failing, what will the built-in test runner report?

Node.js

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

test('test 1', () => {
  assert.strictEqual(1, 1);
});

test('test 2', () => {
  assert.strictEqual(1, 2);
});

A The report shows 2 tests run: 1 passed, 1 failed with AssertionError details.

B The report shows 2 tests run: both passed.

C The report shows 1 test run: the first test only.

D The report crashes and shows no output.

💡 Hint

Check how the test runner handles multiple tests with failures.

The runner executes both tests, reports one pass and one failure with error details.