Test Runner
ELI5 — The Vibe Check
A test runner is the thing that actually runs your tests and tells you which ones passed and which ones failed. It's like the referee in a sports match — it watches all the action, blows the whistle when something goes wrong, and gives you the final score.
Real Talk
A test runner is a tool that discovers, executes, and reports on test suites. It handles configuration, parallel execution, coverage collection, watch mode, and output formatting. Popular JS test runners include Jest, Vitest, and Mocha.
When You'll Hear This
"Which test runner does this project use — Jest or Vitest?" / "Configure the test runner to only run tests in the /src directory."
Related Terms
Coverage
Coverage tells you what percentage of your code is actually tested. 80% coverage means 80% of your lines are touched by at least one test.
Jest
Jest is the most popular JavaScript testing framework.
Mocha
Mocha is an older, flexible JavaScript test runner that lets you pick your own assertion library and mocking tools.
Test Suite
A test suite is just a collection of related tests grouped together.
Vitest
Vitest is a blazing-fast test runner built on Vite. If Jest is the reliable sedan, Vitest is the electric sports car — same driving experience, 10x faster.