Bitcoin Core Development – What does this functional testing involve?

You can run functional tests individually or run a test runner that runs all functional tests.

From Jon Atack’s article on how to compile Bitcoin Core and run tests:

test/functional/test_runner.py To run the standard test suite (try test/functional/test_runner.py -j 60 (or use a similarly high number to run your tests faster in parallel)

test/functional/.py To run individual test files

test/functional/test_runner.py --extended To run the extended test suite

test/functional/test_runner.py --help To see different options for running tests: