Testing of combined modules of an application to determine whether they are
functionally working correctly. The ‘parts’ can be code modules, individual
applications, client and server applications on a network, etc.

Types of Integration Testing:
1. Big Bang: In this approach, all or most of the developed modules are coupled
together to form a complete software system or major part of the system and then used
for integration testing. The Big Bang method is very effective for saving time in the
integration testing process.

2. Bottom up Testing: This is an approach of integration testing where the lowest level
components are tested first, then used to facilitate the testing of higher level components. The
process is repeated until the component at the top of the hierarchy is tested.

All the bottom or low-level modules, procedures or functions are integrated and then tested.
After the integration testing of lower level integrated modules, the next level of modules will be
formed and can be used for integration testing.

3. Top down Testing: This is an approach of integration testing where the top level
modules are tested and the branch of the module is tested step by step until the end of the
related module.

4. Sandwich Testing: This is an approach of combination of both top down testing with bottom up testing.