Testing your network is more then just going to a speedtest site and checking your bandwidth. Network performance also involves latency and jitter.
Latency is how long each network operation takes to accomplish. A typical web page takes 20-100+ operations to complete before its done loading. So how long each one takes really adds up and dominates your experience. Today web page loads are slowed by latency more then bandwidth ( speed ) issues. Latency effects everything you do on the net as its each operation from a keystroke while gaming to using a VPN to watching/listening to a stream involves lots of network operations per second.
Jitter is how much latency jumps around. So if latency varies radically jumping from 10 seconds to sometimes as low as .001 second to do each operation then it has high jitter. Jitter makes the internet experience random and frustrating, for some applications like gaming, its fatal as you die in game from jitter.
A "speed" test is almost meaningless to a typical user these days as latency has become the real issue.
Until mid 2017 latency and jitter HAVE NOT BEEN TESTED DURING CHIP MANUFACTURING OR MODEM/ROUTER MANUFACTURING. THERE IS NOT EVEN A STANDARD. This has led to manufacturers and ISPs ignoring this issue completely.
Some chip makers have hidden issues from the ping command. Ping CANNOT be used reliably to test for latency or jitter. The tests below use TCP
Latency and jitter can come from lots of things on your network. Wifi has horrible latency and jitter VS a wired connection. To improve your experience PLUG IN. You can run the tests below to check your network for latency and jitter. Some of these tests are easy and some are more in-depth. You should do these tests plugged into your network.
Make sure nothing is running on your computer and you are plugged in with a wire for the below tests to be accurate
DSLReports Puma 6 test
A simple, easy and fast single test is the Puma 6 test at DSLReports. While it was designed to spot a Intel Puma 6 - it shows any variations in latency on a network in a great simple to look at graphic. Simply follow instructions on the page. Your result should be a even green, variations in color indicate jitter.
Puma 6 Test Forum thread for discussion
Near perfect result
Bad result showing big spikes in latency
This is a expensive tool - but is free for 2 weeks - Download here - Setup and use instructions are here
Its results are really conclusive. It can spot about any networking performance issue
To isolate a issue using Pingplotter start at your modem/router plugging directly into it with nothing else hooked up to your router/modem. Make sure nothing is running on your computer. Do a plot. If the issue is there then its the router/modem or ISP. If the problem is gone, hook things back up and go back to your normal setup until you find something that causes the issue to appear.