how to test the RAM on a 13" 2019 Macbook Pro

Trackpad issues can also be caused by a swollen battery (at least on older models, not sure if it still applies to the USB-C Macs).

Here is an Apple article with instructions for accessing the Apple Diagnostics....most likely the diagnostics won't detect an issue.

You could try a PRAM Reset (hold for two chimes if possible....sometimes it won't do a second chime) and an SMC Reset (read the instructions since the instructions have changed for 2018-2020 models).

Try booting into Safe Mode to see if that makes a difference.

Disconnect all external devices in case one of them is causing a problem.

Try a firmware "Restore"...should not destroy any data, but make sure you have a good backup first just in case.

Revive or restore an Intel-based Mac using Apple Configurator - Apple Support

It is doubtful any of these will have any effect, but it doesn't hurt to try since otherwise it will most likely be an expensive repair.

Those symptoms are not typical of RAM memory problems. but if you are concerned, you should run the user diagnostics.

You should look at other possible issues.

What comes to my mind is stray input from a trackpad, or if you have a graphics tablet, form a pointer resting on an idle tablet.