Well-tested code prevents regression bugs, simplifies refactoring, and alleviates some of the frustrations that go along with adding new features. Once you've compiled a Wasm module, you should write tests to ensure it's functioning as expected, even if you've written tests for C, C++, or Rust code you compiled it from. In this section, we'll use Jest, a JavaScript testing framework, to test the functions in a compiled Wasm module.