by James McLean.
Thanks for your continued help with this David.
1) Yes, "base_url: 'http://localhost:8000'" is present in the under 'Extensions: Behat\MinkExtension\Extension:'. Those sections are properly formatted.
2) Yes, I have executed that command in the web root directory.
3) Yes, the Moodle instance at that address is titled "Acceptance test site"
I've checked the firewall etc and it isn't blocking that port either.