unit vs functional vs integration tests code example

Example: functional testing vs integration 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.

Functional testing is a kind of black-box
testing that is performed to confirm that
the functionality of an application or 
system is behaving as expected.

 It is done to verify all the functionality 
 of an application works as expected