A bug was found in the product that the test cases did not highlight.
Of course it was. QA cannot guarantee that we can find all the bugs in a product. It simply can't be done. That means there is always a high chance that a bug escapes QA and makes it to production. These tend to be regression bugs. That's OK! What's important is how you deal with those bugs.
First, no one should blame QA for missing a bug. This is detrimental to a safe team environment. As humans, anything we create is flawed. Software is complicated and it's really difficult to test an unlimited set of pathways and integration points software creates.
So, how does QA handle a bug that escaped to production? Before you do anything else, you need to understand how it happened. Here you have some options:
- Perform a root cause analysis. This needs to be done to fix the bug anyway, so QA needs to know how the bug was caused so they can update their test cases.
- Use 5 Whys. This can be really effective in finding the cause in a short amount of time.
Questions to ask yourself in this situation:
- Was the bug directly related to the feature/story being tested?
- Did you only test the requirements/acceptance criteria directly, one-for-one? Did you go beyond what's listed as a requirement?
- Did you test the integration points of that feature? What other features touch the feature you are testing?
- Was the bug in the UI, API, backend?
- Did you do any regression testing?
- Do you have any test automation that covers this feature? If not, can you write an automated test to cover this bug?
- Does your test cases cover the positive/happy path? Do they cover the negative paths? Do they cover edge cases and corner cases?
- Are you performing only black-box testing? Or are you doing any gray-box and white-box testing?
So really, the answer to the OPs question is #1 and #2. You should never do nothing. And whether your test cases are written down in a test case management system or are automated test scripts, you should always update them if bugs are found. They are living documents and you want to assure quality for the long term.