--SOLVED-- Golang accessing variable across same package: import cycle not allowed in test, undefined: variable

My structure is the following:

1. In my db.go, I initialize my database

package database
type Database struct {
    Dbpool *pgxpool.Pool
}
var Db Database
func InitDb() {
    dbpool, err := pgxpool.New(...)
    if err != nil {...} // Check for creating connection
    Db = Database{Dbpool: dbpool}
    greeting, err := Db.GetHelloWorld()
    if err != nil {...} // Check for entering db
}

2. In my queries.go, I create my handlers like my GetHelloWorldhandler for testing purposes

package database

func (db *Database) GetHelloWorld() (string, error) {
    var greeting string
    err := db.Dbpool.QueryRow(context.Background(), "select 'Hello, world!'").Scan(&greeting)
    if err != nil {...} // Check for error in selecting Hello World
    return greeting, err
}

3. So far everything works as expected. Now in my queries_test.go, I like to test my handlers via dockertest in a separate database.

package database

var TestDB Database
var dbpool *pgxpool.Pool
 
func TestMain(m *testing.M) {
    // set up docker container, database and its connection
    dbpool, err = pgxpool.New(...)
    // once everything is set up I want to initialize the database like in db.go
    TestDB = Database{Dbpool: dbpool}
}
func Test_GetHelloWorld(t *testing.T) {
    var greeting string
    greeting, err := TestDB.GetHelloWorld()
}

Everything works in my queries_test.go if I use the dbpool.QueryRow(context.Background(), "select 'Hello, world!'").Scan(&greeting) command in my test as it is written down in my handlers but this is not really the sense of testing handlers...

If I run go test ./queries_test.go like shown above, I have no compile error but inside my testing container I get the error undefined: Database. If I try importing TestDB from db.go like

import app/database 
var TestDB database.Database

I receive the import cycle not allowed in test, which I completely understand is not the way of doing it.
So far I assume a third and maybe forth file with an interface might do the job like suggested here but does it really have to be that complicated?
I feel like there should be a simpler way...
Maybe anyone can help me out?