What do you do when the application you are testing suddenly start to return errors such as…

What do you do when the application you are testing suddenly start to return errors such as 400,401,500, 501, 502,503…?

1. Reproduce Consistently

• Use tools like Postman, cURL, or browser dev tools to isolate and reproduce the issue.
• Check which exact inputs, endpoints, or actions trigger the error.

2. Check Logs and Console

• Review backend/server logs and API gateway logs if accessible.
• Inspect browser console or network tab for additional context.

3. Check Authentication & Tokens (401)

• Ensure tokens or credentials are valid and not expired.
• Verify the correct authentication scheme is being used.

4. Validate the Request Structure (400)

• Ensure the payload is valid (JSON/XML format, required fields present).
• Confirm headers (like Content-Type, Accept, etc.) are correct.

5. Confirm Resource Availability (404)

• Double-check endpoint paths and query parameters.
• Ensure the resource actually exists in the test data/environment.

6. Investigate Server/Infra Issues (5xx Series)

• Check server status and health.
• Look for recent deployments, configuration changes, or known outages.
• Communicate with the DevOps/Backend team.

7. Document and Report

• Create detailed bug reports:

1. Steps to reproduce
2. Expected vs. actual results
3. Screenshots/logs
4. Error codes/messages
5. Prioritize based on impact and frequency.