Bottom Up Testing

What is Bottom Up Testing?

Each component at lower hierarchy is tested individually and then the components that rely upon these components are tested.

Bottom Up Integration - Flow Diagram

The order of Integration by Bottom-down approach will be:

4,2
5,2
6,3
7,3
2,1
3,1

Testing Approach :

+ Firstly, Test 4,5,6,7 individually using drivers.
+ Test 2 such that it calls 4 and 5 separately. If an error occurs we know that the problem is in one of the modules.
+ Test 1 such that it calls 3 and If an error occurs we know that the problem is in 3 or in the interface between 1 and 3

Though Top level components are the most important, yet tested last using this strategy. In Bottom-up approach, the Components 2 and 3 are replaced by drivers while testing components 4,5,6,7. They are generally more complex than stubs.