Mocha & Chai

Summary

A flexible, unopinionated test runner (Mocha) commonly paired with an assertion library (Chai) — an older but still widely used alternative to Jest in many Node.js codebases.

• 1Set up Mocha + Chai and write a test equivalent to one you wrote in Jest.
• 2Compare Chai's `expect`/`should` assertion styles to Jest's built-in `expect`.
• 3Understand why some existing codebases still use Mocha+Chai over Jest.