How do you test route endpoints with PHPUnit?

I am starting out with PHPUnit in a small project of mine, and the very first test I'd like to write is the one that hits an index.php script (or very soon, a route endpoint) and examines the response. In particular, I'd like to assert that the response body (i.e. HTML) contains a string, such as 'Hello World'. For such as trivial task,

• How do I instruct PHPUnit to make a GET request to a script/route?
• Does PHPUnit offer any facilities to perform HTTP tests?
• Do I have no choice but to use something like Guzzle?

Note, I do not want to mock the response (or the request for that matter). I want to perform an actual HTTP request and get an actual response from the server. Also,

• Would I need to instruct PHPUnit (through phpunit.xml?) to bootstrap my application behind the scenes before making any requests?

PHPUnit newbie here, sorry for the very basic question. Any help'd be appreciated!