While chrome developer tools allow you to test for many http post vulnerabilities relating to invalid post data, testing for a slow post vulnerability needs Googles slowhttptest tool.
The installation in very straight forward
As the docs say, you'll need lib-ssldev. When missing you'll get:
configure: error: OpenSSL-devel is missing
My LMDE does not have this out of the box, though Synaptic delivered.
After the make, running slowhttptest hits up localhost by default. Nothing interesting without a local test server.
Shekyan also includes the syntax to launch an example of the SLOWORIS attach to test on your own servers.
./slowhttptest -c 1000 -H -g -o my_header_stats -i 10 -r 200 -t GET -u https://localhost/index.html -x 24 -p 3