Coverage for multiple packages in go

Prelude

There is awesome coverage in go. You can read about it here. But also it has some limitations. For example let’s assume that we have next code structure:

src
├── pkg1
│   ├── pkg11
│   └── pkg12
└── pkg2
    ├── pkg21
    └── pkg22

pkg2, pkg21, pkg22 uses pkg1, pkg11 and pkg12 in different cases. So question is – how we can compute overall coverage for our code base?

Generating cover profiles

Let’s consider some possible go test commands with -coveprofile:

go test -coverprofile=cover.out pkg2

tests run only for pkg1 and cover profile generated only for pkg2

go test -coverprofile=cover.out -coverpkg=./... pkg2

tests run only for pkg2 and cover profile generated for all packages

go test -coverprofile=cover.out -coverpkg=./... ./...

boo hoo: cannot use test profile flag with multiple packages

So, what we can do for running tests on all packages and get cover profile for all packages?

Merging cover profiles

Now we able to get overall profile for each package individually. It seems that we can merge this files. Profile file has next structure, according to cover code:

// First line is "mode: foo", where foo is "set", "count", or "atomic".
// Rest of file is in the format
//      encoding/base64/base64.go:34.44,37.40 3 1
// where the fields are: name.go:line.column,line.column numberOfStatements count

So, using magic of awk I found next solution to this problem:

go test -coverprofile=pkg1.cover.out -coverpkg=./... pkg1
go test -coverprofile=pkg11.cover.out -coverpkg=./... pkg1/pkg11
go test -coverprofile=pkg12.cover.out -coverpkg=./... pkg1/pkg12
go test -coverprofile=pkg2.cover.out -coverpkg=./... pkg2
go test -coverprofile=pkg21.cover.out -coverpkg=./... pkg2/pkg21
go test -coverprofile=pkg22.cover.out -coverpkg=./... pkg2/pkg22
echo "mode: set" > coverage.out && cat *.cover.out | grep -v mode: | sort -r | \
awk '{if($1 != last) {print $0;last=$1}}' >> coverage.out

The true meaning of last line I leave as an exercise for user :) Now we have profile for all code, that was executed by all tests. We can use this merged profile coverage.out for go cover tool:

go tool cover -html=coverage.out

or for generating cobertura report:

gocover-cobertura < coverage.txt > coverage.xml

Conclusion

Of course this solution is only workaround. And it works only for mode: set. Similar logic must be embedded to cover tool. I am really hope that one day we will be able to run

go test -coverprofile=cover.out -coverpkg=./... ./...

and leaning back in chair, enjoying perfect cover profiles.