Require‑Hijack is a lightweight Node.js utility that lets developers mock entire `require`‑d modules—replacing a module’s exported class, function, or object—in unit tests. It works by intercepting `require` calls via require‑middleware without touching the module cache, making it suitable for mocking built‑in modules (e.g., `fs`) or any dependency before the tested code is loaded. Ideal for developers who need fine‑grained, full‑module mocking in their test suites.