v.com/main
-- vendor/v.com/main/main.go --
package main

// #cgo CFLAGS: -I../c
// #include "stdio.h"
// void printfile();
import "C"

func main() {
    C.printfile()
    C.fflush(C.stdout)
}
-- vendor/v.com/main/foo.c --
#include "bar.h"
-- vendor/v.com/c/bar.h --
#include "stdio.h"

void printfile() {
    printf("%s\n", __FILE__);
}
-- main/main.go --
package main

// #cgo CFLAGS: -I../c

-- main.go --
package main

import "runtime"

func PrintFile() {
	_, file, _, _ := runtime.Caller(0)
	println(file)
}

-- main_test.go --
package main

import (
	"runtime"
	"testing"
)

func PrintFileForTest() {
	_, file, _, _ := runtime.Caller(0)
	println(file)
}

func TestMain(m *testing.M) {
	PrintFile()
	PrintFileForTest()

package pkg_test

import "runtime"

func PrintFile() {
	_, file, _, _ := runtime.Caller(0)
	println(file)
}

-- pkg_x_test.go --
package pkg_test_test

import (
	"runtime"
	"testing"

	"example.com/pkg_test"
)

func PrintFileForTest() {
	_, file, _, _ := runtime.Caller(0)
	println(file)
}

func TestMain(m *testing.M) {
	pkg_test.PrintFile()
	PrintFileForTest()

[short] skip

go test -trimpath -v .
! stdout '[/\\]pkg_test[/\\]'
stdout -count=3 '[/\\]pkg[/\\]'

-- go.mod --
module example.com/pkg

go 1.17

-- pkg.go --
package pkg

import "runtime"

func PrintFile() {
	_, file, _, _ := runtime.Caller(0)
	println(file)
}

-- pkg_test.go --
package pkg

import "runtime"

func PrintFileForTest() {
	_, file, _, _ := runtime.Caller(0)
	println(file)
}

        expect:
        (1..4).each {
            def givenText = "[$it] Hello World!"
            inputFile.text = givenText
            run "printFile"
            executedAndNotSkipped(":printFile")
            outputContains(givenText)
            assert originalInputFileLength == inputFile.length()
        }

        where: