On Ubuntu or other Linux distribution, you can easily install radtest using
sudo apt -y install freeradius-utils
After that, you need to create a Router representing your test PC on the MikroTik device so that RADIUS requests will be accepted.
Now you can run radtest like this:
radtest -t mschap [Username of the user to authenticate] [Password of the user to authenticate] [MikroTik IP] 1812 [Router shared secret]
Note the Router shared secret is the password that you used when setting up the Router instance for radtest in User manager -> Routers before and not the router’s admin password etc.
1812 is the default (and recommended) port for RADIUS.