Basics

go test tests packages as it is stated below.

> go test -h
test [build/test flags] [packages] [build/test flags & test binary flags]

So given a package, go test runs both in package tests and outside package tests.

> go test github.com/haibin/coverage/person
ok  	github.com/haibin/coverage/person	0.007s

To list in package tests, run the following.

> go list -f '{{.TestGoFiles}}' github.com/haibin/coverage/person
[foo_test.go]

To list outside package tests, run the following.

> go list -f '{{.XTestGoFiles}}' github.com/haibin/coverage/person
[person_test.go]

Test Coverage

To show a summary of test coverage, run the following

> go test -cover github.com/haibin/coverage/person
ok  	github.com/haibin/coverage/person	0.005s	coverage: 75.0% of statements

According to the go test doc on -coverpkg, The default is for each test to analyze only the package being tested. so the above command is the same as the below.

> go test -coverpkg github.com/haibin/coverage/person github.com/haibin/coverage/person
ok  	github.com/haibin/coverage/person	0.006s	coverage: 75.0% of statements in github.com/haibin/coverage/person

Now we have some integration tests outside of the package github.com/haibin/coverage/person but we want to see how much more coverage those tests provide to the same package.

> go test -coverpkg github.com/haibin/coverage/person github.com/haibin/coverage/it
warning: no packages being tested depend on github.com/haibin/coverage/person
ok  	github.com/haibin/coverage/it	0.006s	coverage: 25.0% of statements in github.com/haibin/coverage/person

We can run them together as below.

> go test -coverpkg github.com/haibin/coverage/person github.com/haibin/coverage/it github.com/haibin/coverage/person
ok  	github.com/haibin/coverage/it	0.005s	coverage: 25.0% of statements in github.com/haibin/coverage/person
ok  	github.com/haibin/coverage/person	0.005s	coverage: 75.0% of statements in github.com/haibin/coverage/person

So what is the total coverage? There might be some overlapping of tests in github.com/haibin/coverage/it and tests in github.com/haibin/coverage/person. Let’s generate coverage profile.

> go test -coverprofile=coverage.out -coverpkg github.com/haibin/coverage/person github.com/haibin/coverage/it github.com/haibin/coverage/person
cannot use test profile flag with multiple packages

We got this cannot use test profile flag with multiple packages error. So we have to run it one by one.

> go test -coverprofile=it.out -coverpkg github.com/haibin/coverage/person github.com/haibin/coverage/it
warning: no packages being tested depend on github.com/haibin/coverage/person
ok  	github.com/haibin/coverage/it	0.006s	coverage: 25.0% of statements in github.com/haibin/coverage/person

> go test -coverprofile=person.out -coverpkg github.com/haibin/coverage/person github.com/haibin/coverage/person
ok  	github.com/haibin/coverage/person	0.006s	coverage: 75.0% of statements in github.com/haibin/coverage/person

Then we merge the two profiles.

> github.com/wadey/gocovmerge
> gocovmerge person.out it.out > coverage.out

And we get the total coverage!

> go tool cover -func=coverage.out
github.com/haibin/coverage/person/person.go:4:	Age		100.0%
github.com/haibin/coverage/person/person.go:9:	Name		100.0%
github.com/haibin/coverage/person/person.go:14:	City		100.0%
github.com/haibin/coverage/person/person.go:18:	foo		100.0%
total:						(statements)	100.0%