Checkpoint: Why and What to Test

Five questions on this section. Answer all of them, then see your score and why each answer is right or wrong.

A user reports that splitting a $100.00 dinner between three people leaves the balances one cent off. Which test do you write first?

A Playwright test that adds the dinner in the browser and reads the balances.
A screenshot test of the balances screen.
A stricter TypeScript type for the amount parameter.
A unit test that splits 10000 cents between 3 people and checks the shares add up to 10000.

Assuming the imports are in place, what happens when this test runs?

JavaScript

test('formats cents', () => {
  expect(formatMoney(1234)).toEqual('$12.34');
  expect(formatMoney(5)).toBe('$0.05');
});

It passes if formatMoney is correct: toEqual compares primitives by value, just like toBe.
It fails, because toEqual can only be used with objects.
It fails, because a test may contain only one expect.
It only runs when globals: true is set in the config.

Your package.json has "test": "vitest", and the GitHub Actions job runs npm test. What happens after the tests finish in CI?

The job hangs in watch mode until it hits the runner timeout.
Vitest exits with an error asking for the --run flag.
Vitest notices the CI environment variable, runs once and exits with the result.
Vitest skips the tests because no terminal is attached.

A test fails with this output. What is the most likely bug?

Text

FAIL  src/tip.test.js > withTip > adds a 15% tip
AssertionError: expected { tipCents: 300, totalCents: 2000 }
  to deeply equal { tipCents: 300, totalCents: 2300 }

The tip is rounded the wrong way.
The test should use toBe instead of toEqual.
The percent is divided by 1000 instead of 100.
The total is returned without adding the tip.

Your project has 300 tests of pure money logic and 5 test files that render DOM. How should you configure the environment?

Set environment: 'jsdom' globally so every test can use the DOM.
Keep the default Node environment and add // @vitest-environment jsdom to the top of the 5 DOM test files.
Stub document with a plain object in a setup file.
Move the 5 DOM tests to Playwright.

5 questions unanswered