Load Testing Junior interview questions and answers

75 questions for a Load Testing (Junior) interview - with correct answers, explanations and links to the docs.

Take this quiz
  1. 1.What is the main goal of a load test?
  2. 2.How does a stress test differ from a load test?
  3. 3.What does a spike test check?
  4. 4.What is a soak (endurance) test for?
  5. 5.In k6 terms, what is a smoke test?
  6. 6.What does a breakpoint test do?
  7. 7.What does throughput usually mean in load testing?
  8. 8.What is latency (response time) of a request?
  9. 9.What does "p95 response time = 400 ms" mean?
  10. 10.Why are percentiles preferred over the average response time?
  11. 11.Which percentile equals the median?
  12. 12.What is the error rate in a load test report?
  13. 13.What is a virtual user (VU) in a load testing tool?
  14. 14.What is think time in a load test script?
  15. 15.Why do load tests usually start with a ramp-up instead of full load at once?
  16. 16.In a k6 script, what does the exported default function contain?
  17. 17.What load does this k6 configuration create?
  18. 18.What does this stages setting describe?
  19. 19.What does check() do in k6?
  20. 20.What is a threshold in k6?
  21. 21.A k6 run has 30% failed checks but no thresholds. What exit code does k6 return?
  22. 22.Which built-in k6 metric holds the total time of an HTTP request?
  23. 23.What does the k6 metric http_req_failed measure by default?
  24. 24.What does the iterations metric in a k6 summary count?
  25. 25.How do you run a k6 script from the command line?
  26. 26.In JMeter, what does a Thread Group define?
  27. 27.What is a sampler in JMeter?
  28. 28.Why should real JMeter load tests run in CLI (non-GUI) mode?
  29. 29.What does this JMeter command do?
  30. 30.In which language do you write Locust tests?
  31. 31.Why should a load test environment be close to production?
  32. 32.What is a performance baseline?
  33. 33.Why is "100 concurrent users" not the same as "100 requests per second"?
  34. 34.What is a bottleneck in performance testing?
  35. 35.Why monitor server CPU, memory and DB during a load test?
  36. 36.The load generator's CPU is at 100% during a test. What does that mean for the results?
  37. 37.Why should a load test not reuse a single user and product ID for every request?
  38. 38.What is parameterization in a load test script?
  39. 39.What is correlation in a load test script?
  40. 40.Why exclude the first minute or two of a test from the analysis?
  41. 41.What is an SLO in the context of performance?
  42. 42.A service handles 50 requests per second, and each takes 0.2 s on average. How many requests are in progress at once on average?
  43. 43.What does scalability mean for a system?
  44. 44.What is horizontal scaling?
  45. 45.Under load, the API starts returning 429. What does it mean?
  46. 46.What does a 503 response during a load test usually indicate?
  47. 47.How are timeouts usually counted in load test results?
  48. 48.How does performance testing relate to load testing?
  49. 49.Why must a load test against a shared or production environment be agreed in advance?
  50. 50.Where should the target load for a load test come from?
  51. 51.Is a Lighthouse audit a load test?
  52. 52.Which k6 metric is closest to time to first byte (TTFB)?
  53. 53.Why add sleep(1) at the end of a k6 iteration?
  54. 54.What does group() do in k6?
  55. 55.Why add tags to k6 requests?
  56. 56.When does setup() run in k6?
  57. 57.How do you read an environment variable in a k6 script?
  58. 58.How can you send k6 results to a file or a monitoring system?
  59. 59.The max response time is 9 s, but p99 is 350 ms. How do you read it?
  60. 60.What is the steady state of a load test?
  61. 61.Load grows, throughput stops growing, and latency rises sharply. What is happening?
  62. 62.Why can results from two runs differ even with the same script?
  63. 63.Under load, DB queries are fast but the app waits for a connection. What is the likely bottleneck?
  64. 64.What is a workload model?
  65. 65.What is tail latency?
  66. 66.The server returns 200 with an error page under load. How do you catch it?
  67. 67.What kind of load test fits into a CI pipeline on every pull request?
  68. 68.What does a Response Assertion in JMeter do?
  69. 69.What is a Timer used for in JMeter?
  70. 70.What does volume testing focus on?
  71. 71.The CPU of an API server is at 30% while latency is high. Which is a likely cause?
  72. 72.Why include the network location of load generators in the test plan?
  73. 73.What does teardown() in k6 do?
  74. 74.Which three metrics does the RED method look at for each service?
  75. 75.Why is a single run at full load not enough to call a system ready?