added tests for db and user

Backend/models/booking.go

@@ -30,7 +30,12 @@ type Booking struct {
 	CounterId  int       `json:"counter_id"`
 }
 
-var DB *sql.DB
+type IDatabase interface {
+	Prepare(query string) (*sql.Stmt, error)
+	Exec(query string, args ...any) (sql.Result, error)
+}
+
+var DB IDatabase
 
 func (b *Booking) New(card_uid string, geraet_id int16, check_in_out int16) Booking {
 	return Booking{