Bottom Up Integration

Bottom-up integration testing begins construction and testing with atomic modules (i.e. components at the lowest levels in the program structure). Because components are integrated from the bottom up, processing required for components subordinate to a given level is always available and the need for stubs is eliminated.

1. A Bottom-up integration strategy may be implemented with the following steps:
2. Low level components are combined into clusters that perform a specific software sub function.
3. A driver is written to coordinate test case input and output.
4. The cluster is tested.

Drivers are removed and clusters are combined moving upward in the program structure.