How do you test a component that fetches data and shows loading and error states?

What the interviewer is looking for

• This question tests frontend testing. Tests user-visible behaviour, mocks network calls sensibly, and balances component tests with a few end to end tests.
• Strong answers: Mocking the network layer, testing what the user sees rather than internals, covering loading, success, empty and error states, and avoiding flaky timing.
• Likely follow-up: When would you add an end to end test on top of that?

Another way it may be asked: You've built a user profile card that loads from an API. How would you write tests that check it behaves properly in every case?

A structure to follow: Answer, explain, example, limits

1. Step 1

   Answer

   Give your direct answer in the first sentence so the interviewer knows where you are going.

2. Step 2

   Explain

   Say how it works or why you would do it that way, in plain words before jargon.

3. Step 3

   Example

   Anchor it in something you have actually done or seen, with the detail that shows hands-on experience.

4. Step 4

   Limits

   Say when your approach would not be the right one. It shows judgement.

This is guidance on shape, not a script. Use your own real experience and facts; never invent details to fill a gap. See the STAR guide and answer frameworks.

Common slips

• Reciting a definition without showing you have applied it.
• Using terms you cannot explain if asked a level deeper.
• Claiming experience beyond what you can discuss in detail.

How to practise it

Say the answer in 90 seconds, then answer the follow-up as if it were a new question.

Related questions

• How would you build a layout that looks good on both a phone and a wide desktop screen? Talk me through your approach.
• Can you explain what happens when you await a promise in JavaScript, and how you handle errors from it?
• What are some simple things you do to make sure a form can be used by someone on a screen reader or only a keyboard?
• How do you decide where a piece of state should live in a React or similar app, and when do you reach for a global store?
• A product page feels slow to load on mobile. How would you find out why, and what would you try first?

Browse all questions