You might need to simulate crappy wifi, or spotty cell or otherwise "there but just barely or not really" network connectivity, so as to make sure your app or whatevz handles that gracefully.
Presuming your server is on linux, this is the long and short of it:
# add a rule limiting bandwidth and adding latency
# to the network interface serving your thing
# mine is 'enp2s0', but maybe yours is 'eth0'