The software testing can be dividing into four levels (unit, integration, system and acceptance). In each level, different approaches are used and different characteristics are tested, if you want you can check V-model.
In this post I will only give you an short overview about the level, I will introduce more details in a future post.
Before I start explain the level, I need to point that test level are represented using a pyramid because for healthy software testing approach you need to respect balance between the tests.
Unit test
The unit tests have the purpose of finding faults in units of software. The units can be a class, a function, an object, or even just a method or procedure.
This is the first level of the test to be executed in the application, in which the white-box method approach is usually used.
Integration test
The integration tests are intended to test the internal interaction and communication between the various components of the Software.
At this level of testing, the most common errors found are related to the transmission of data between these components:
- Interface misuse: Bad interface usage of a component calls for another component and makes an error in the use of its interface
- Interface misunderstanding: The component sends the request and misunderstands the specification of the interface of the component receiving the request and makes assumptions about its behaviour. The called component does not behave as expected which then causes unexpected behaviour.
- Timing errors: These occur in systems that use a shared memory or data. When a system requests data, it can be outdated or inexistent.
The integration tests are mostly black-box but sometimes can be white-box.
System tests
The system tests test the system as a whole, where the hardware and software are integrated. The main objective of this level of testing is to ensure that the system behaves according to specifications.
In this level, for the first time, the non-functional requirements of the product are tested.
These tests are black-box.
Acceptance tests
Acceptance tests are the last tests to be conducted before it is sent to production. The application is tested in an environment where it will be used.
These tests are black-box.
