If you ever have worked in a large project you have probably seen that there are multiple .vsmdi-files under sourcecontrol after a while. These files contains information about the testruns in the project and if the current file is checked out to another developer you will create a new such file if you change the testrun.
There is a good reason for not having these files under sourcecontrol.
Almost all developers have their own way of viewing files and especilly testruns and if this file is checked in and somebody makes a change that change will affect all other developers when they perform a "get latest"
The below blogpost is very informativ in specifying in how you can remove these files from sourcecontrol and make it possible for every developer to create their own testruns.