Get coverage per test

Using coverlet.core, is it possible to get a “parent line” for a specific hit, to determine the call stack of the covered line?

I want to use that to figure out which tests ran through a specific line.

[petli]

I’ve been curious about getting per-test coverage reports since the file formats tend to support it, but it would require a fair bit of redesign of the hit collection and a challenge to do it efficiently. Right now there is a single int[] per module that the hits are recorded into.

My rough idea of what’s necessary to do to create this is that you have to change how methods are instrumented so that on entry they locate the unit test (if any). This would be done by traversing the callstack up, and then cache the result in an AsyncLocal so it doesn’t have to be done by every nested instrumented method. A hit array is created for each unit test, and used in the instrumented code instead of the static array that’s currently injected.

When the test is done all these hit arrays would have to be transferred over to the coverlet process. This is already a time critical operation that is only stable when using the vstest collector driver, so moving potentially thousands of hit arrays would only be feasible in that driver, excluding the standalone and msbuild drivers as it stands now.

Finally the coverlet core will need to collate these hit arrays to get per-test statistics.

[petli]

If it’s not possible to figure out which tests ran through a specific line, could it perhaps be possible to generate a coverage file per test in the test run?

You could do this by scripting your test runs. dotnet test -t lists the tests in a project and iterate over them in a script, and then your script can run test by test by running dotnet test --filter "$testname" --other-parameters-as-needed-to-get-coverage. This will not be very efficient, of course.