What's the theory of GET test of a domain?

Question

What's the theory of speed test website's GET test?

In the 17ce site:

I input the domain cnblogs.com in it, and use GET request test.

it will test the speed.

one of the test point I click the GET button shows:

HTTP/1.1 301 Moved Permanently
Date: Thu, 05 Sep 2019 07:19:44 GMT
Content-Length: 0
Connection: close
Location: https://www.cnblogs.com/

HTTP/1.1 200 OK
Date: Thu, 05 Sep 2019 07:19:44 GMT
Content-Type: text/html; charset=utf-8
Transfer-Encoding: chunked
Connection: close
Vary: Accept-Encoding
Cache-Control: public,max-age=30
Age: 11
Content-Encoding: gzip

!snapshot

I want to know what's the theory of the GET test?

Is it download the https://www.cnblogs.com/index page for calculation?