Top down Integration Test
1)program and tested from the top to the bottom
2)The modules are integrated by moving downward through the control hierarchy, beginning with the main control module Ref. fig 1
3)The modules subordinate to the main control module are incorporated into the structure in either a depth or breadth first way first.
Integrated Testing is done in an environment that closely resembles that of reality, so the tested product is more reliable
Stubs are functionally simpler than drivers, and therefore can be written with less time and labor
Basic functionality test at the end of cycle
Start building and testing with atomic modules (ie modules of the lowest levels in the structure of the program.
Fuses and tested program from the bottom upwards.
The terminal module is tested in isolation first, then the next set of higher level modules are tested with the lower pre-tested modules.
Programming and testing operations can be performed simultaneously, obtaining noticeable improvements in the efficiency of software development
Unit Testing of each module can do very well
Key interface defects trapped at the end of cycle
Test drivers have to be generated for modules at all levels except the top control
We can test the program in the real environment in which to run.
One type of integration testing in which software components are combined in one application at a time on a global system.Under this approach, each unit module is first tested in isolation of each module. After each module is tested, all modules are integrated together at once..