Code Coverage in Go Tests: Using covdata to Combine Profiles

I think one of my biggest adventures with Go has been working with tests. They changed one of my opinions about the language’s pragmatism: yes, it is still super practical, still very simple and pleasant to program in, but I used to take that idea too lightly, to the point of doing things any which way and without respecting software engineering principles. As the name says, they are principles; they do not depend on the language, and Go is not exempt from them.

Maybe I will explore that idea more in another article, but in this one I want to show how I managed to combine unit test and integration test coverage.

It turns out that the tool that analyzes code coverage does not separate test suites, so infrastructure-only code, which would be covered by an integration test, still goes into the same analysis as the unit tests. What I wanted to avoid was running integration tests together with unit tests because of a limitation in a third-party tool (Sonar, cough, cough…).

And the Go ecosystem surprised me once again: there is a tool from Go itself that helps in these cases, covdata: https://pkg.go.dev/cmd/covdata

The first step was to separate unit tests from integration tests. I have been using make to keep these executions handy:

.PHONY: unit-test
unit-test:
	go test -short -cover ./contract/... ./internal/cli/... ./internal/http/... -test.gocoverdir="${PWD}/test/cover/unit"

.PHONY: integration-test
integration-test:
	go test -short -cover ./internal/infra/... -test.gocoverdir="${PWD}/test/cover/integration"

Then add a step that merges the two coverage profiles:

.PHONY: cover
cover:
	go tool covdata textfmt -i=./test/cover/unit,./test/cover/integration -o cover.out

Now we can send the cover.out file to Sonar analysis:

sonar.go.coverage.reportPaths=cover.out

It combines the coverage from the unit tests and the integration tests.

The integration tests use Testcontainers BTW, so here is a tip for another great tool: https://testcontainers.com.