6.5 Integration Testing:

Once the entire module have undergone unit testing they are integrated and again tested for bugs using a technique called integration testing.
There are two methods: incremental and non incremental integration. In non incremental integration the tendency is to construct the program using “Big Bang Approach”.
Two different incremental strategies are: Top down and Bottom up integration.
6.5.1 Top down Integration:
Top down testing is incremental approach. Modules /components are integrated by moving downwards through control hierarchy, beginning with main control module.

6.5.2 Bottom up Integration
Bottom up testing begins construction and testing with automatic modules. Because modules are integrated from the bottom up processing required for modules subroutines to a given level is always available and the need for stubs is eliminated.
The steps of bottom up integration strategy:
• Low level modules are combined into clusters that perform a specific software sub function.
• A driver is written to co-ordinate test case input and output.
• The cluster is tested.