os.IsNotExist but getting "not a directory"

I can not understand, why I am not able to create a folder and write to a file, and then read it in again - with the same path in same func, just for testing? <br>
When I run "go test myio_test.go" on the file. I get

myio_test.go

...
func TestMyIo(t *testing.T) {

	myio.CreateTempJsonFile()
}
....

myio.go

package myio

import (
	"fmt"
	"io/ioutil"
	"path"
	//"syscall"
	// "os"
	"bitbucket.org/kardianos/osext"
	"os"
)

func CreateTempJsonFile() {

	exePath, _ := osext.Executable()
	filePath := path.Dir(exePath + "/json/")
	fmt.Println("create: ", filePath)

	_, errx := os.Stat(filePath)
	if os.IsNotExist(errx) {
		errm := os.Mkdir(filePath, 0644)
		if errm != nil {
			fmt.Println("error creating dir...")
			panic(errm)
		}
	}

	writeError := ioutil.WriteFile(filePath+"/user.txt", []byte(`{"user": "Mac"}`), 0644) // os.ModeTemporary)// 0644)
	if writeError == nil {
		fmt.Println("Ok write")
	} else {
		fmt.Println("Error write")
	}

	_, err := ioutil.ReadFile(filePath + "/user.txt")
	if err == nil {
		fmt.Println("Reading file")
	} else {
		fmt.Println("Error reading file")
	}
}

It is like the os.Stat(filePath) thinks the folder is already there. If I then remove the check for os.Stat() and just go and create the folder I get a panic "not a directory
"?

fmt.Println("create: ", filePath) prints:

/private/var/folders/yj/jcyhsxxj6ml3tdfkp9gd2wpr0000gq/T/go-build627785093/command-line-arguments/_test/myio.test/json

It is all strange, as each test creates a new "/go-buildxxx/" folder and therefore the folder should never actually be there?

Any ideas?

First, you need to split off the executable from it's base path as it's returned from osext

exePath, _ := osext.Executable()
base, _ := filepath.Split(exePath)

(or use osext.ExecutableFolder())

Then you need to create the directory with the permissions 0755. Directories need the executable bit set in order to traverse them.