5 Integration Testing

Once classes have been successfully unit tested, there must be a clear, well-defined strategy in place for combining them together incrementally to form the final product. If the whole system is simply combined together after Unit Testing (the Big Bang approach) and there is a bug, it will not be easy to find the bug. Hence, the system will be built incrementally, and tested at each stage. This is, in effect, the build plan, which has been represented here as Integration Testing, and in particular, the Order of Integration. Integration Testing is designed to ensure that the classes interface with each other correctly (as defined in the DDD), and hence is mainly concerned with the interfaces between classes (and not the internal workings of classes). Once subsystems have been built, Integration Testing also tests that each subsystem as a whole is performing its responsibilities. Before any Integration Tests are applied to classes, these classes must have passed all their Unit Tests.

As with Unit Tests, Integration Tests will be written using PyUnit (see section 14.1) or with Mtest (see section 6), and run using the runtests script (see section 1.7).