vs 2008 unit testing prompt meaning

i'm unit testing in vs2008 and every time i run now it says

    Executing the current test run will produce a new test run result, which will exceed
 the limit of 25 that is curren开发者_高级运维tly specified. If you continue, older test run results and
 their associated deployments will be deleted from the hard drive...

what does this mean, and how do i clear the older test run results? why is this important message?

This message basically means that the Unit Test project has saved/recorded 25 (your threshold) results of previously run unit tests.

By proceeding, it'll remove one from those 25 to include the results of your next run.

You can modify the 'alert' here in the Tools->Options dialog:

You can modify this number here: