Top Down Integration Testing

What is Top-Down Integration Testing ?

Top-down integration testing is an integration testing technique used in order to simulate the behaviour of the lower-level modules that are not yet integrated. Stubs are the modules that act as temporary replacement for a called module and give the same output as that of the actual product.

The replacement for the 'called' modules is known as 'Stubs' and is also used when the software needs to interact with an external system.

Stub - Flow Diagram:

The above diagrams clearly states that Modules 1, 2 and 3 are available for integration, whereas, below modules are still under development that cannot be integrated at this point of time. Hence, Stubs are used to test the modules. The order of Integration will be:

1,2
1,3
2,Stub 1
2,Stub 2
3,Stub 3
3,Stub 4

Testing Approach:

+ Firstly, the integration between the modules 1,2 and 3
+ Test the integration between the module 2 and stub 1,stub 2
+ Test the integration between the module 3 and stub 3,stub 4