In top down integration approach we need to wite stubs and driver code example

Example 1: what is 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.

Example 2: top down vs bottom up testing

Top-Down testing begins with the system and 
works its way down to the unit level.
• Bottom-up testing checks in the opposite
direction, unit level to interface to
overall system. Both have value but
bottom-up testing usually aids in discovering
defects earlier in the development cycle, 
when the cost to fix errors is lower.