Per-test coverage in Go

Question

I am building a Go provider for Pruner (a CLI that runs only the tests that ran through the lines you changed, saving you time).

For that, I need to be able to see per-test coverage. Not just a full coverage report after all tests have run, but I need a way to know which tests ran through what line.

Is that possible in Go?

I tried using -func, but it just gives me the method names of the original code, not the test code. In other words, I can't know what code each individual test runs through.

Answer 1

I need a way to know which tests ran through what line.

Is that possible in Go?

It's not supported by the tools. But you can do it. It's just very inefficient.

The way to do this is to run:

go test -cover -run=TheName/OfSome/SpecificTest

Then run this for each test in your suite.

Naturally, this will make your tests much more cumersome to manage, and incredibly slow.

So I would consider whether this is truly a requrement for your use case.

Go is optimized, from the ground-up, to compile quickly. If you have a Go project so long, that running all the tests is too slow, you may want to consider other alternatives. Some suggestions:

1. Run more tests in parallel, so the total runtime is reduced.
2. Take advantage of Short mode, and only run short tests by default, saving long-running tests for special cases.
3. If you really need to run only a subset of tests, do it on a per-package basis, not on a per-test basis.