go test causes no such file or directory

I'm creating a RESTFull API in Go and securing my application with JWT. I'm using ECDSA algorithm so I have private and public key pair. In order to create a JWT token I have to read them.

First of all this is my project structure:

.
├── Dockerfile
├── Makefile
├── config
│   └── config.go
├── config.json
├── data
│   ├── init.sql
│   ├── keys
│   │   ├── 256
│   │   │   ├── keys-256.md
│   │   │   ├── private-key.pem
│   │   │   └── public-key.pem
│   │   └── 512
│   │       ├── keys-512.md
│   │       ├── private-key.pem
│   │       └── public-key.pem
│   └── ....
├── go.mod
├── go.sum
├── handler
│   ├── auth.go
│   ├── auth_test.go
│   ├── healthcheck.go
│   └── healthcheck_test.go
│   
├── main.go
└── security
    └── token
        ├── generator.go
        └── parser.go

This is the source file where I read private key file as you can see I'm using init function in go so I'll read the key file once and use it every time I need it.

generator.go

package security

import (
	"crypto/ecdsa"
	"fmt"
	"io/ioutil"
	"log"
	"net/http"
	"strconv"
	"time"

	"github.com/golang-jwt/jwt"
    // ...
)

var privateKeyPath = "data/keys/512/private-key.pem"
var privateKey *ecdsa.PrivateKey

func init() {
    printWorkingDirectory()
	privateKey = getECDSAPrivateKey(readPrivateKeyFile())
}



func getECDSAPrivateKey(data []byte) *ecdsa.PrivateKey {
        ecdsaKey, err := jwt.ParseECPrivateKeyFromPEM(data);
	if  err != nil {
		log.Fatalf("Unable to parse ECDSA private key: %v", err)
	}
	return ecdsaKey
}

func readPrivateKeyFile() []byte {
	data, err := ioutil.ReadFile(privateKeyPath)
	if err != nil {
		log.Fatalf("Can not read private key file: %v", err)
	}
	return data;
}
func printWorkingDirectory() {
	mydir, err := os.Getwd()
	if err != nil {
		fmt.Println(err)
	}
	fmt.Println("Working directory: ", mydir)
}
//...

Key path is relative to root directory of project var privateKeyPath = "data/keys/512/private-key.pem"

When I run go run . in the root directory, everything fine.

When I run go test ./... Golang creates a temporary directory and runs my test in there basically this causes a problem.
Here is the result of go test ./...:

✗ go test -v ./...

Working directory is:  /var/folders/wk/ncyvbtdj3w57cr5j1v46x7dr39dz_l/T/go-build4211274972/b150
Initing db manger
2021/10/28 19:13:47 Can not read private key file: open data/keys/512/private-key.pem: no such file or directory
FAIL    mydomain/myprojectname/handler   1.274s

Actually I'm a Java Developer and I'm new in Go

Simply in Java we have classpath and it saves the day.

I don't want to use absolute path because I have Dockerfile and if I use absolute path in my local computer it will hurt me in docker container.

My question is:

How can I use a relative path which works with go run and go test commands.

The problem you are facing is because when you run go run, or for that matter when you run your built application, the working directory is inherited from your environment. But when a package is tested, the working directory is always the package directory.

One quick solution would be to have a copy of your data directory inside your security directory as a test fixture, this would also allow you to use a specific key for testing.

A better solution is to think about how you will load your key in production. This init() function in your security package is quite inflexible because:

1. In production, your key must be in a specific location relative to the working directory only.
2. You cannot influence the behaviour of the init() function in tests because init() is always run before tests start.

My recommendation would be that rather than using init(), you pass either the literal key, or a path to the key into class/classes in the security package from main when you instantiate them. This way your key can be located anywhere when in production and your tests can be directed to use a key in the source tree relative to that package's directory.