As introduced at the beginning of this section, there is no an universal definition for the different forms of testing. In this section we review some of the most commonly varieties of testing available in the literature not covered so far. For instance, when the testing process is performed to determine whether the system meets its specifications, it is known as conformance testing. When a new feature or functionality is introduced to a system (we can call it a build), the way of testing this new feature in known as progression testing. In addition to that, to check that the new introduced changes do not affect the correctness of the rest of the system, the existing test cases are exercised. This approach is commonly known as regression testing.

When the system interacts with any external or third-party system, another testing could be done, known as system integration testing. This kind of testing verifies that the system is integrated to any external systems properly.

User or customer testing is a stage in the testing process in which users or customers provide input and advice for system testing. Acceptance testing is a type of user testing, but there can also be different types of user testing:

• Alpha testing: This takes place at developers' sites, working together with the software's consumers, before it is released to external users or customers.
• Beta testing: This takes place at customer's sites and involves testing by a group of customers who use the system at their own locations and provide feedback, before the system is released to other customers.
• Operational testing: This is performed by the end user in its normal operating environment.

Finally, release testing refers to the process of testing a particular release of a system performed by a separate team outside the development team. The primary goal of the release testing process is to convince the supplier of the system that is good enough for use.