How to write unit test for CommonsMultipartFile with Mock

file type need to be org.springframework.web.multipart.MultipartFile. This is the super interface above CommonsMultiPartFile and MockMultipartFile. If you have done this, then you can create a mock of the multipart file itself with an mock object that is provided by spring, just like below:
MockMultipartFile mockMultipartFile = new MockMultipartFile(String name, String originalFilename, String contentType, byte[] content);

you can get more information from http://stackoverflow.com/questions/8799378/how-to-write-unit-test-for-commonsmultipartfile-with-mock-in-spring