Install Docker and run the following command!
1) docker run --restart=unless-stopped --name=openspeedtest -d -p 80:8080 openspeedtest/latest
This can run offline! So you can use it to test your Local Area Network or put it on a server to test your line speed to that server. Currently optimised to test speeds up to 1~2 Gbps. You can change the values and files inside this docker and can test even faster connection.