A test suite that passes and an app that works are not guaranteed to be the same thing, and the gap between them is usually explained by what level the tests were actually written at. A component test that renders a form and asserts its internal state object looks correct can pass while the actual rendered text on screen is wrong, because it never checked what a real user would actually see or touch. The uncomfortable fact this lesson starts from is that a test's value is bounded by how closely it resembles what a user actually does, not by how much of the code's internals it happens to exercise.
React Native testing spans three genuinely different layers doing three genuinely different jobs: Jest runs fast, isolated unit and component tests in a simulated JavaScript environment with mocked native modules; React Native Testing Library (RNTL) sits on top of Jest and encourages writing those component tests the way a user actually interacts with the screen, by text and role rather than by internal implementation detail; and Detox runs slow, realistic end-to-end tests against a genuinely compiled app on a simulator or emulator, exercising real navigation, real native modules, and real timing. None of the three replaces the others, and a team that only invests in one layer inherits that layer's specific blind spot.
Analogy🏏Cricket
🏏 Think of it like cricket: A bowler's preparation for a Test series happens at three genuinely different intensities, each catching a different kind of flaw. Bowling machines and throwdowns in the nets check basic mechanics in a controlled, low-stakes setting, fast and repeatable, but they cannot reveal how a bowler actually reacts under a real batter's footwork and real match pressure. A full simulated net session against the actual batting lineup, at closer to match intensity, reveals more about matchups and plans but still isn't the real thing. Only an actual tour match, in genuinely foreign conditions with a genuinely unfamiliar pitch, reveals whether the preparation holds up completely. Ravichandran Ashwin's preparation before overseas tours has always moved through exactly these three intensities, because skipping any one of them leaves a specific class of problem undiscovered until the real Test match. Just as a bowling machine session and a tour match catch different flaws at different cost, a Jest unit test and a Detox end-to-end test catch different flaws at different cost. Just as skipping the tour match entirely means discovering a conditions-specific weakness only in the actual Test, skipping end-to-end tests entirely means discovering a real-device, real-navigation bug only in production. The insight is that no single level of preparation substitutes for the others — each one is cheap insurance against a specific class of failure the others cannot see.
🏏 Showing the Cricket analogy — a Cricket version isn’t available for this concept yet.