integration tests vs unit tests vs system tests code example

Example: integration testing vs system testing

Integration testing is done to test the
modules when integrated to verify that they
work as expected. to test the modules which are
working fine individually don't have
issues when they are integrated.

System Testing means testing the system
as a whole. All the modules/components 
are integrated in order to verify if 
the system works as expected or not.

System Testing is done after Integration Testing.
Main idea is the delivering high quality product.