It is an interview question, and I did not know how to tackle it. do I go to DevTools and check its performance? what kind of tools do I use?
Be honest with the interviewer and about knowing your own experiences, skills, and what you are lacking. If you know you have missing skills and can admit it in an interview, this shows self-awareness. Self-awareness is not a weakness, but shows confidence! A lot of people will say "make something up" or "just fake it," but that tends to show with a lack of confidence. And if you get the job and they expect you to do performance testing, then you're playing from behind and still need to own up to not knowing this skill. So, it's best to be honest upfront. Areas where you a lacking, be sure to also answer with how you plan on learning about this skill!
Now, if you have some knowledge, then answer with what you know. You seem to know about performance testing features in the browser dev tools. It seems like your perspective is on the front-end or with web apps. So your answer is:
"While I don't have a lot of experience in performance testing, I do know it's an important skill to have. What I've done in the past is to open the browser's DevTools and use the Performance Profiler. I also have used Google's Lighthouse to perform a comprehensive report. I take the information I learn and work with the dev team on correcting the issues found."
You can also give more details on how you work with the dev team. Is it just informal conversations about your findings? Are you writing bugs or stories for these concerns? Are you running a discovery meeting with the team to go over solutions? Explain these details. This is how you give a comprehensive answer that shows your knowledge, skills you're willing to learn, how you work with a team, how you share knowledge, etc. And when you're comprehensive like this, your confidence will come through!
Remember, interviewers aren't necessarily looking for a "perfect" answer, but they do want you to extrapolate on your skills, experience, how you work on a team, how you learn, etc.
Other aspects to this question:
Performance testing can be done at any level of software: web apps/front-end, backend, APIs, databases, etc. So, a more experienced answer should include these areas.
If you have any knowledge of performance testing tools/services, regardless of if you've used them, you can answer with those as well. Something like:
"I don't have a lot of experience, but I do know about tools like JMeter, K6, etc. There are both local tools and cloud-based tools."
Here, you can give details on the pros/cons of the differences between local/cloud tools. You can also do a cost-benefit analysis of free/open-source tools versus paid tools.
You can also ask the interviewer to clarify what they mean by performance: what level of the stack? Are they looking for stress testing, load testing, soak testing, etc?
Interviewers tend to give broad/general questions, so it's up to you to ask for clarification. Some interviewers ask questions because they are in need of certain skill sets immediately. So, this allows you to pry into what problems they are having. In addition to the above, you can also ask them:
- Is the team experiencing performance issues currently? What are they?
- Are customers complaining/leaving due to performance issues?
- Does the team use any performance testing tools currently?
- How is DevOps involved with performance testing? (At some companies, QA doesn't do performance testing, but DevOps will!)
- Do you expect performance testing to be done in production or in non-production environments? (This allows you to determine the level of risk they are willing to accept!)
- Are you willing to pay for tools to help with performance testing?
- Are there any monitoring tools setup to log or alert on performance issues in production?
Hopefully, this helps for next time you encounter this question. And, points you in a direction to learn new skills!
By using browser developer tools you can only inspect individual requests response times using "Network" tab and get in-depth information on page loading, rendering and scripts execution timings using "Performance" tab. See https://profiler.firefox.com/ for example
All above applies only to frontend, if you need to assess your web app performance under the load (when it's being used by multiple users at the same time) you will need a load testing tool which is capable of simulating real users activities.