Why does Visual Studio create a new .vsmdi file?

Question

If I open a solution in Visual Studio 2008 and run a unit test then VS creates a new .vsmdi file in the Solution Items folder and gives it the next number available e.g. My Solu

Answer 1

Assuming that the VSMDI file is under source control, here's a Microsoft Support article about this issue: Multiple vsmdi Files after Running Team Test with VSMDI file under Source Control

Which says:

Someone ran a test while someone else was modifying the vsmdi file. Team Test detects that the VSMDI file is out of sync;therefore, Team Test it makes one and thus you see the incrementing vsmdi files.

And:

Going forward you want to make sure the file is not marked for auto checkout when it is modified. When the current tester has the VSMDI file checked out you, do not want other users to be able to check it out. You want your developers to checkout the file, run a test, and check it back in.