How did you verify the correctness of your work?

On a recent bug fix, I changed the logic that calculated shipping cost for small orders. To verify it was correct, I first wrote a couple of tests around the exact cases from the bug report, and then I added edge cases like a zero-dollar order and a value right at the free-shipping threshold. After that, I ran the app locally and checked that the total shown in the UI matched the numbers I calculated by hand. Once it was deployed, I looked at a few real orders in production and confirmed the totals were now correct there too. That gave me confidence I hadn't just fixed the narrow case, but the actual behavior users cared about.

At my last internship, I added a simple admin page that let our support team update a user’s contact information. To make sure it worked, I first tested it with a few made-up accounts in our staging environment and tried both valid and invalid inputs, like empty phone numbers and badly formatted email addresses. I also asked the support lead to walk through the flow with me, because they were the person who would actually use it every day and could tell me if anything felt confusing. After that, I checked the database directly to confirm the changes were saved exactly as expected and that the old values were replaced. I liked this approach because it wasn’t just about “does the code run,” but about whether the feature was reliable for the people who depended on it.