Unit testing and integration testing:

Unit testing focuses on the least element of software design by the module. Unit test is conducted on every of the modules to uncover errors within the boundary of the module. It becomes easy when a module is designed to perform only one function.  Unit testing makes heavy use of white-box testing.

Integration testing is a systematic approach for constructing program structure whereas conducting tests to uncover errors associated with interfacing. There are likely to be interfacing problems, such as data mismatch among the modules. In Incremental integration the program is constructed and tested in small segments.