How do I know the code my AI assistant wrote is actually correct?

LLMs produce code that passes unit tests but satisfies no formal properties. A model can construct tests that pass by construction, not because the logic is right. Formal verification tools exist but require writing specifications in theorem-prover syntax, which almost no working developer does. Recent benchmarks show that frontier models achieve only 3.2 percent success on end-to-end verifiable code generation, meaning the gap between plausible-looking code and proven-correct code is nearly entirely open. Teams shipping AI-written code into production are making a bet on test coverage that the models themselves can game.