From nwpotago:

At https://docs.moodle.org/dev/Running_acceptance_test in the "Prerequisite" section, there are three links to sections within https://docs.moodle.org/dev/Acceptance_testing - which now redirects to the Running_acceptance_test page, rendering the links invalid.

Where is the current documentation on behat prerequisites?

It should be linked from the "Prerequisite" section of https://docs.moodle.org/dev/Running_acceptance_test