黑盒子的Golang测试覆盖率_test coverage

My problem is simple, but the answer remains elusive. Suppose I have a package

package mypackage

func DoTheThing() int {
  return 5
}

Now suppose I have a test using in the mypackage_test package

package mypackage_test

import "testing"
import . "mypackage"

func TestDoTheThing(t *testing.T) {
    if DoTheThing() != 5 {
        t.Error("there was a problem")
    }
}

Now I want to know the code coverage of the package mypackage.

$ go test -cover
PASS
coverage: 0.0% of statements
ok      /my/path/mypackage 0.002s

It should be 100%. I have tried also

$ go test -v -cover -coverpkg ./... ./...
=== RUN   TestDoTheThing
--- PASS: TestDoTheThing (0.00s)
PASS
coverage: 0.0% of statements in ./...
ok      /my/path/mypackage 0.002s  coverage: 0.0% of statements in ./...

It is not a possibility for me to include the test in mypackage, so I need to know the code coverage of mypackage in this setup.

Thanks for your time.

After much keyboard mashing, I discovered it has to do with the fact that I was simlinking my project directory to $GOPATH/src/.

Copying the project into $GOPATH/src/mypackage and running go test -cover correctly returns 100% coverage.