Unit Testing tests to make sure functionality is working as expected in the system. This does not take into consideration other integration points. Includes testing specific configuration items.
Integration testing tests required process flows and all related integration points in the system. This includes testing multiple configuration settings.
User Acceptance testing this testing involves bringing in individuals from different parts of the business to test specific functionality.
System testing these tests focus on testing system functionality instead of business process flows. Sometimes, it is important to test integration with legacy or third party applications.
Stress testing stress testing involves testing the system on performance imitating real-life load scenarios on the system. This can alter system sizing requirements.
Regression Testing involves testing already implemented functionality and processes to make sure they are not impacted by an upgrade, installation, enhancement, or some other change in the system that could cause an impact.