You can run tests to validate your modifications.
Post PR #10291, py.test is used as the test runner. Testing dependencies are in requirements-test.txt, so pip install -r requirements-test.txt first.
Most of the tests run against a live instance of the WebUI. You can start the WebUI server with a suitable baseline configuration with the --test-server argument, but you may want to add e.g. --use-cpu all --no-half depending on your system.
The command to run webui tests is: python -m pytest -vv --verify-base-url test