Install into your test project

dotnet add package AltCover

and run

dotnet test /p:AltCover=true

The OpenCover format output will be in file coverage.xml in the project directory

The instrumentation process needs to find one of the dependencies to do its work. In the latter case, the assembly was found in the default user-level NuGet cache location; in the former, either the AltCover build is too old, the assembly isn't in the default NuGet cache location, or the wrong version was found.

Running

dotnet test /p:AltCover="true" /p:CopyLocalLockFileAssemblies="true"

may resolve the issue.

If this doesn't work, or doing the equivalent of a dotnet publish into the binaries folder interferes with your downstream process, update to the latest (or at least >= v4.0.653 for the latest enhancements) AltCover build and use the /p:AltCoverDependencyList= parameter instead to point to the assembly or assemblies in question.

Choose one or both of LCov or Cobertura like this

dotnet test /p:AltCover=true /p:AltCoverCobertura=<path to file> /p:AltCoverLcovReport=<path to file>

or

dotnet test /p:AltCover=true /p:AltCoverOpenCover=false

for NCover format

Use the /p:AltCoverAssemblyExcludeFilter MSBuild property to exclude the test-related assemblies (unit tests, test runners) from coverage, while still fixing up linkage and supporting test call tracking.

MSBuild MySolution.sln
cd <Unit Test project $(OutputDir)>
<path to>/AltCover.exe
cd ./__Instrumented

and run unit tests against the files there.

Under some versions of Mono on non-Windows platforms, with old-school projects, the default values of --debug:full or --debug:pdbonly generate no symbols from F# projects -- and without symbols, such assemblies cannot be instrumented. Unlike with C# projects, where the substitution appears to be automatic, to use the necessary --debug:portable option involves explicitly hand editing the old-school .fsproj file to have <DebugType>portable</DebugType>.

You probably need to read the full usage guide.