How QA Engineers Actually Test a Login Feature From UI to API

A practical walkthrough published on DEV Community demonstrates how software QA professionals test a login feature across UI, API, and automation layers within a real sprint workflow. The guide covers key test scenarios including the happy path, boundary conditions such as exactly five failed login attempts triggering an account lockout, and edge cases like SQL-injection-style inputs and session persistence. It emphasizes testing at the API level first, arguing that UI-only test suites can miss critical regressions like a broken lockout threshold even when the interface appears normal. The article provides sample Python code using Selenium and a Page Object pattern to automate high-value, stable test cases. Manual exploratory testing is recommended for usability observations that require human judgment rather than automated pass/fail assertions.