The Levels of Software Testing

A piece of software is more than several lines of code. It is usually a multilayer, complex system, incorporating dozens of separate functional components and third-party integrations. Therefore, efficient software testing should go far beyond just finding errors in the source code. Typically, the testing covers the following levels of software.

·         Component/Unit Testing

The smallest testable part of the software system is often referred to as a unit. Therefore, this testing level is aimed at examining every single unit of a software system in order to make sure that it meets the original requirements and functions as expected. Unit testing is commonly performed early in the development process by the engineers themselves, not the testing team.

·         Integration Testing

The objective of the next testing level is to verify whether the combined units work well together as a group. Integration testing is aimed at detecting the flaws in the interactions between the units within a module. There are two main approaches to this testing: bottom-up and top-down methods. The bottom-up integration testing starts with unit tests, successively increasing the complexity of the software modules under test. The top-down method takes the opposite approach, focusing on high-level combinations first and examining the simple ones later.

·         System Testing

At this level, a complete software system is tested as a whole. This stage serves to verify the product’s compliance with the functional and technical requirements and overall quality standards. System testing should be performed by a highly professional testing team in an environment as close to the real business use scenario as possible.

·         User Acceptance Testing

This is the last stage of the testing process, where the product is validated against the end user requirements and for accuracy. This final step helps the team decide if the product is ready to be shipped or not. While small issues should be detected and resolved earlier in the process, this testing level focuses on overall system quality, from content and UI to performance issues. The acceptance stage might be followed by an alpha and beta testing, allowing a small number of actual users to try out the software before it is officially released.

In Agile software development, the testing typically represents an iterative process. While the levels generally refer to the complete product, they can also be applied to every added feature. In this case, every small unit of the new functionality is being verified. Then the engineers check the interconnections between these units, the way the feature integrates with the rest of the system and if the new update is ready to be shipped.