Visual Studio Ultimate has a “Web performance Test” feature that allows you to specify the number of times a test is run. But it looks like it runs those tests one after another. eg if you specify 100 it ill run the test 100 times in a row.

Is it possible to run the 100 tests at the same time in order to stress test the web app? And if not, what does Visual Studio provide that can be use for stress testing?
When using VS Ultimate, you can perform a number of tests on a web application.
From here:
In this case, you will want to create a stress test using the New Load Test Wizard.
Hope it helps!