A local Selenium
The simplest way to get a local selenuim installation is using docker. The following docker invocation is from https://github.com/SeleniumHQ/docker-selenium
docker run -d -p 4444:4444 \ -p 5902:5900 \ -v /dev/shm:/dev/shm \ selenium/standalone-chrome-debug:3.12.0-cobalt
This will also let you login over VNC to see the browser run in the test session which is extremely handy when you are developing new unit tests. The password to connect to vnc is the word secret by default.
Running the tests locally
To run the Selenium tests against your local docker image you will need to edit your config/config.php file. Note that the test suite makes some changes to that file so making a backup of the file before you start is a great idea.
Then edit your config/config.php and set $testing to true. This will enable fake authentication and set some configuration settings which are used by the test suite. If you do not already have a $testing in there look at the config/config_sample.php from git master and copy the $testingsection into your config.php. You should make sure to have a copy of all the config settings in the $testing for your release (or newer) in your config.php.
As mentioned, you need to allow the test suite write access to config.php for things to work (chmod +w for apache) which is obviously bad in production but not too bad for a test only instance.
Then you can run individual Selenium tests with the following command, picking the exact test class to execute.
phpunit --debug \ --configuration unittests/config.xml \ unittests/selenium_tests/UploadAutoResumeTest.php