unit testing vs functional testing vs integration testing code example

Example 1: unit test vs functional test

Unit Tests are written from a programmers
perspective. It is executed to ensure that
a particular component of an application 
performs a set of specific tasks.

Functional Tests are written from the user
perspective. They ensure that the system
is functioning as users are expecting.
Functional testing is a BlackBox testing
technique that is usually performed by the tester.

Unit Testing of software applications 
is done during the development (coding)
of an application. UNIT Testing is defined
as a type of software testing where
individual units/components of a 
software are tested.

Example 2: 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