Unit Testing Fundamentals with Jest
The core building blocks of writing unit tests — test/describe blocks, assertions with expect, and the arrange-act-assert structure — using Jest as the representative framework.
Unit testing verifies that an individual piece of code — typically a single function or a small, isolated module — behaves correctly in isolation, and Jest (one of the most widely used JavaScript testing frameworks) provides the standard vocabulary most developers use to write these tests, making fluency with its core API a practical, everyday interview expectation rather than a niche or advanced topic.
Unit tests are like a series of small, automated inspections on an assembly line: instead of a human periodically eyeballing finished products for defects, a machine automatically checks a very specific measurement (one assertion) on every single unit that passes by, immediately flagging exactly which measurement failed and by how much, rather than a vague 'something seems off' after the fact.