Safari + WebDriver aka SafariDriver comes included in Safari 10 which means as long as you have Safari 10 and later versions you can point your tests at Safari and run them without installing anything else.
Safari now provides native support for the WebDriver API. Starting with Safari 10 on OS X El Capitan and macOS Sierra, Safari comes bundled with a new driver implementation that’s maintained by the Web Developer Experience team at Apple. Safari’s driver is launchable via the
/usr/bin/safaridriverexecutable, and most client libraries provided by Selenium will automatically launch the driver this way without further configuration. – WebKit Announcement
That’s right, no brew installs and no system PATH setups!