What is the correct order of various levels of testings?

The correct order of various levels of testing is Unit testing: This type of testing considers the internal logic and check whether single unit is working well or not. So, it is the first level. Integration testing: It checks the integrity of the modules and concentrates on functional requirements which is done after individual units are tested. So, it comes after unit testing. System testing: It is done to verify whether entire system is working according to requirement or not. So, it comes after checking the integrity of modules. Acceptance testing: It is done to know whether the system is read for acceptance by the user. So, it is a final level.