Test Runner / Test Framework

Tools like pytest, JUnit, Jest or Vitest that find, run and report tests.

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Also known as: test framework, testing framework, pytest, JUnit, Jest, Vitest

A test runner (or test framework) is the tool that finds your tests, runs them, and reports which passed or failed. Some test libraries bundle assertions, setup helpers and a runner; others split them.

Language	Common choices
Python	pytest, unittest
JavaScript / TypeScript	Jest, Vitest, Mocha, Node’s built-in `node:test`
Java	JUnit, TestNG
Go	the built-in `go test`
Ruby	RSpec, Minitest

# test_cart.py: pytest finds files and functions named test_*
def test_empty_cart_total_is_zero():
    assert Cart().total() == 0

pytest                    # run everything
pytest tests/test_cart.py # one file
pytest -k "empty"         # tests whose name matches
pytest -x                 # stop at the first failure

What a runner gives you

Discovery: finds tests by naming convention, so you don’t list them by hand.
Isolation: a failing test doesn’t stop the others.
Reporting: which tests failed, with the assertion and a diff of expected vs actual.
Setup and teardown helpers (fixtures).
Extras: running tests in parallel, watching files, coverage (test coverage), filtering by name or tag.

Tips

Learn your runner’s commands for running a single test and for stopping on the first failure. You’ll use them constantly while debugging.
Run the full suite before you push; CI will run it again.
Pick the runner your project already uses. Consistency beats preference.