By default DevPartner does not enable the merge of coverage files from two different executables.
There is a undocumented switch that can be used: The /a switch Sample test run C:\test>nmmerge /a /d . /m output.dpmrg c:\test\HelloWorld1.dpcov c:\test\HelloWorld2.dpcov Loading c:\test\HelloWorld1.dpcov... Done Merging c:\test\HelloWorld2.dpcov... Done