Discover the often-overlooked chapter in the testing book: thoughtfully choosing the inputs we pass in our tests. How crucial is this? The parameters and data passed to the API/functions under test will determine our tests' coverage, reliability, and speed. It's too easy to miss critical paths when having many combinations of inputs and config, or when using synthetic unrealistic data. Dive into an exhilarating journey that combines wisdom from cutting-edge AI, open-source libraries, classic books and just common sense. Don't like theoretical talks? Great, because 90% of our time will get spent with real-world testing scenarios and popular libraries (OSS). Expect code demos of techniques like equivalence class, LLM clustering, data factories, fuzzers, pair-wise, and more. My duty on stage is not just to tell what is possible, but rather to emphasize mature techniques and how to succeed wit each. This talk is based on my testing best practices guides online (5+ million visitors)