Is it possible to get the current root of package structure as a string in golang test?

I am writing a utility function for my unit tests which is used by unit tests in multiple packages. This utility function must read a particular file (always the same file). Here are three solutions which do not work, to explain what I am looking for and why.

1. Hardcode the absolute path. This fails because another user who is trying to test the project might have a different prefix on the absolute path.

2. Hardcode a relative path from the path of the file which defines the utility function. This fails because packages which import and use this function are not necessarily at the same level of the file hierarchy as the file that defines the utility function, and relative paths are interpreted relative to the importer, not the imported.

3. Pass in the relative path to the file from every caller relative to the caller's package. This actually works but seems to be very verbose because now every caller must be changed to pass one file.

I see a fourth solution, whereby I can hardcode a path in the utility function which is relative to the root directory of the top-level package. However, I have not been able to find a way to get the root directory in code, although I suspect there is one because imports can be resolved from the root.

Thus, how might I get the sought-after root directory?

I've looked over various Go documents but have so far failed to find a solution. I have also seen this question but the solution there is equivalent to #3 above.

You can also use my method without C:

package mypackage

import (
    "path/filepath"
    "runtime"
    "fmt"
)

var (
    _, b, _, _ = runtime.Caller(0)
    basepath   = filepath.Dir(b)
)

func PrintMyPath() {
    fmt.Println(basepath)
}

https://play.golang.org/p/ifVRIq7Tx0

Building on the answer by Oleksiy you can create a sub-package in your project called ./internal/projectpath/projectpath.go and paste in the following:

package projectpath

import (
	"path/filepath"
	"runtime"
)

var (
	_, b, _, _ = runtime.Caller(0)

	// Root folder of this project
	Root = filepath.Join(filepath.Dir(b), "../..")
)

Then you can use projectpath.Root in any other package to have the root folder of your project.

Returns the root of the application:

import (
	"path"
	"path/filepath"
	"runtime"
)  

func RootDir() string {
	_, b, _, _ := runtime.Caller(0)
	d := path.Join(path.Dir(b))
	return filepath.Dir(d)
}

Go directories:

// from Executable Directory
ex, _ := os.Executable()
fmt.Println("Executable DIR:", filepath.Dir(ex))

// Current working directory
dir, _ := os.Getwd()
fmt.Println("CWD:", dir)

// Relative on runtime DIR:
_, b, _, _ := runtime.Caller(0)
d1 := path.Join(path.Dir(b))
fmt.Println("Relative", d1)

Yes, Finding package path is possible:

pathfind.go:

package main

/*
const char* GetMyPathFILE = __FILE__;
*/
import "C"
import "path/filepath"

var basepath = ""

//GetMyPath Returns the absolute directory of this(pathfind.go) file
func GetMyPath() string {
	if basepath == "" {
		g := C.GoString(C.GetMyPathFILE)
		basepath = filepath.Dir(g)
	}
	return basepath
}

All you have to do is copy this file to your project. Keep in mind this comes up with the path for the file, not the caller so you have to copy the function/file to every project you need the function in. Additionally if you put this in a file with other code be sure to respect CGO's import rules.