Add support for executing coverage via SLN

It’s possible to construct a SLN that contains only test csproj files and then use that to execute all of those csprojs at once. When you then run dotnet test all_my_tests.sln, it will execute your test csprojs in parallel - which is an order of magnitude faster than iterating through, say, a list of all the test projects individually.

I would love to be able to collect coverage this way as well, using the stand-alone tool. Ideally something like: coverlet \tests.sln --target "dotnet" --targetargs "test tests.sln --no-build"

It SORT of works now in that tests start executing. However, it has hiccups when it tries to generate the coverage.json files - probably because they do not have a unique nomenclature. The run abruptly ends with

Calculating coverage result...
  Generating report 'C:\Users\mbenua\Documents\GitHub\server\coverage.json'

+--------+--------+--------+--------+
| Module | Line   | Branch | Method |
+--------+--------+--------+--------+

I suspect there’s not a lot of work to get this scenario working, which would be an ENORMOUS perf improvement. Perhaps only as much as having the option to generate unique coverage filenames?

[ardalis]

Merging results seems to have been done 10 months ago. Now would like to be able to specify a single output file for a .sln so that I can run this from solution root:

dotnet test /p:CollectCoverage=true /p:MergeWith=CoverageResult.json

This would:

• Discover all tests
• Run all tests
• Collect coverage for all tests (and maybe drop the results into their respective folders as it does today)
• New Merge all test results into CoverageResult.json specified.

[MarcoRossignoli]

close because dup of https://github.com/tonerdo/coverlet/issues/357 For merge there is new sample in documentation https://github.com/tonerdo/coverlet/blob/master/Documentation/Examples.md