What is integration testing?

Integration testing is a level of software testing where individual units, modules, or components of a software application are combined and tested as a group. The primary goal of integration testing is to verify the functional, performance, and reliability between the integrated units/components. During the development process, software components are usually developed individually and then integrated to form a complete system or subsystem. Integration testing thus plays a critical role in identifying and addressing interface issues, data flow problems, and other integration errors early in the development cycle. This form of testing can be done in several ways, such as:

1. Big Bang Integration Testing: In this approach, all or most of the units are combined together at once, and the entire system is tested as a whole. This method might be straightforward but can lead to identifying errors being more complicated due to the large number of interacting units.

2. Incremental Integration Testing: Unlike the Big Bang approach, this method involves integrating two or more units that logically related, testing them, then adding another unit to integrate and test, and so on. This can be further classified into:

– Top-down Integration Testing: Testing takes place from top to bottom following the control flow or architectural structure. High-level modules are tested first, then low-level modules and finally integrating the low-level modules to high level to ensure the system is working as intended.

– Bottom-up Integration Testing: This approach starts from the bottom or the lowest level of modules. The lowest modules are tested first