Incremental testing

With incremental testing, you test components as soon as they are available and you create stubs or drivers (some sort of placeholder) for components that are not yet available. There are two approaches here:

• Top-down testing: Using top-down testing would mean I would've checked whether the external service could make a call to the internal service and, if the internal service was not available yet, create a stub that pretends to be the internal service.

• Bottom-up testing: Bottom-up is testing the other way around, so I'd start testing the internal service and create a driver that mimics the external service.

Incremental testing has the advantage that you can start defining tests early before all the components are complete. After that, it becomes a matter of filling in the gaps.