Final assessment

Twelve questions across the whole course. Score 70% or more to pass and unlock your certificate. You can retake it as often as you like.

Finish every lesson to earn the certificate — you can take the assessment any time.

A form parses the amount and sends it through an API client. Which test gives the most confidence per minute of CI for that form?

A component test that renders the form with the real parser and a faked network.
A unit test of the API client alone.
An end-to-end test for every validation message.
Stricter TypeScript types on the form props.

What is the main problem with this test?

JavaScript

test('withTip', () => {
  expect(withTip(2000, 15).tipCents).toBe(300);
  expect(() => withTip(2000, -1)).toThrow();
  expect(withTip(2000, 0).totalCents).toBe(2000);
});

toBe cannot compare numbers reliably.
It checks three behaviours, so a failure in the first hides the others, and the name does not say what broke.
A test may contain only one expect call.
withTip must be awaited.

A group must have between 2 and 12 members. Which inputs test the rule best?

5, 6 and 7
2 and 12
0 and 100
1, 2, 12 and 13

await expect(loadGroup('x', fetchMock)).rejects.toThrow() passes both for the correct code and for a version that crashes with a TypeError before it checks the status. How do you make the test meaningful?

Use resolves instead of rejects.
Add more await keywords around the call.
Match the expected message, for example .rejects.toThrow('HTTP 404').
Replace toThrow with toThrowError.

Tests pass one by one but fail in the full run. An earlier test does vi.spyOn(Math, 'random').mockReturnValue(0). What is the fix?

Restore mocks after each test, with vi.restoreAllMocks() in afterEach or restoreMocks: true in the config.
Run the test files one at a time.
Raise Vitest’s test timeout.
Stop using Math.random in production code.

An icon-only button is rendered as <button aria-label="Delete expense"><svg>…</svg></button>. Which query should a Testing Library test use?

screen.getByText('Delete expense')
screen.getByRole('button', { name: 'Delete expense' })
screen.getByTestId('delete')
container.querySelector('svg').closest('button')

A “Saved” toast appears after saving and disappears a moment later. How do you assert that it disappears?

expect(screen.getByText('Saved')).toBeNull()
expect(await screen.findByText('Saved')).toBeNull()
Sleep 5 seconds, then expect(screen.queryByText('Saved')).toBeNull()
await waitForElementToBeRemoved(() => screen.queryByText('Saved'))

This Playwright check fails now and then in CI. What is the fix?

TypeScript

const rows = await page.getByRole('listitem').all();
expect(rows.length).toBe(3);

Add await page.waitForLoadState('networkidle') before it.
Use await page.getByRole('listitem').count() instead of .all().
await expect(page.getByRole('listitem')).toHaveCount(3)
Set retries: 3 in the config.

End-to-end tests share one seeded group, and one of them deletes an expense from it. Other tests fail depending on the order. What is the best fix?

A fixture that creates a uniquely named group per test through the API and deletes it afterwards.
Run the suite serially in a fixed order.
Reseed the database once before the whole suite.
Enable three retries for those tests.

Which tool tells you that no test would notice if a < in your code became <=?

Line coverage
Branch coverage
The TypeScript compiler
Mutation testing, for example StrykerJS

Pull requests keep getting merged while the end-to-end job is red. What is the right fix?

Rerun the job until it turns green, then merge.
Make the test jobs required status checks on the main branch.
Remove the end-to-end job to keep the pipeline green.
Run the end-to-end job only after merging.

A component test mocks your own pure formatMoney so it always returns 'X'. What is the best change?

Keep the mock and add a snapshot of the output.
Replace the mock with vi.mock on the module.
Use the real formatMoney: it is fast, pure code you own, and the test then checks the real output.
Delete the component test.

12 questions unanswered