MS unit test ( to verify 100 simultaneous requests to server )

In my user interface I have a submit button which submits a request to the server ( thorugh Rest API - say Submit() ) to do some data processing . This works fine . I would like to perform unit test on this ( server data processing code ) to make sure that simultaneous submit requests from different users does not result in any concurrency issues.

How should I go about writing my unit test that would help in verifying that the code works for n simultaneous requests.