I have 5 test projects in my solution. I'm building my test results and code coverage with the script below.
This creates 5 folders in TestResults named like glompix_MACHINENAME 2016-03-11 17_38_57\Out\. You can see the glompix_MACHINENAME_etc.trx, vstest.coveragexml, and emma\coverage.xml files.
However, only part of my solution shows up in code coverage. If I target a single project, it works like a charm. It seems the results aren't being merged correctly.