WebSocket & Async APIs interview questions — Hard
75 hard-level WebSocket & Async APIs questions from our API Testing bank, each with the correct answer and an explanation of why it is correct.
This topic slice is available to practise but is not yet part of our indexed set.
What this covers
WebSocket & Async APIs appears throughout API Testing interviews. At hard level, interviewers are typically checking depth under pressure — edge cases, failure modes, performance characteristics, and the trade-offs you accepted. Work through these, then explain your answer out loud; the second part is what interviews actually test.
4 example questions
1. Regarding WebSocket, which of the following is a false statement?
- A. Message queues can only be tested with a web browser.correct
- B. Load testing WebSockets measures concurrent connection capacity and message latency.
- C. Server-Sent Events (SSE) stream data one-way from server to client.
- D. Testing WebSockets involves validating connection lifecycle, message order, and reconnection behavior.
Why: The selected statement is false. The other options are accurate statements about WebSocket.
2. Which of the following statements about WebSocket is FALSE?
- A. WebSocket connections close automatically after every single message.correct
- B. Server-Sent Events (SSE) stream data one-way from server to client.
- C. Testing WebSockets involves validating connection lifecycle, message order, and reconnection behavior.
- D. Load testing WebSockets measures concurrent connection capacity and message latency.
Why: The selected statement is false. The other options are accurate statements about WebSocket.
3. Identify the INCORRECT statement about WebSocket:
- A. Message-driven systems are often tested by publishing to and consuming from queues or topics.
- B. WebSockets allow only the client to send messages, never the server.correct
- C. Server-Sent Events (SSE) stream data one-way from server to client.
- D. Testing WebSockets involves validating connection lifecycle, message order, and reconnection behavior.
Why: The selected statement is false. The other options are accurate statements about WebSocket.
4. Which statement about WebSocket is NOT correct?
- A. A WebSocket connection starts as an HTTP request upgraded via the Upgrade header.
- B. Testing WebSockets involves validating connection lifecycle, message order, and reconnection behavior.
- C. WebSocket provides full-duplex, persistent communication over a single TCP connection.
- D. Server-Sent Events allow the client to stream data to the server.correct
Why: The selected statement is false. The other options are accurate statements about WebSocket.