diff --git a/crates/backend/Cargo.toml b/crates/backend/Cargo.toml
index ed04113..f6da6fd 100644
--- a/crates/backend/Cargo.toml
+++ b/crates/backend/Cargo.toml
@@ -29,5 +29,9 @@ uuid = "1"
 
 dotenvy = "0.15"
 
+[dev-dependencies]
+temp-env = "*"
+
+
 [features]
 serve = []
diff --git a/crates/backend/src/main.rs b/crates/backend/src/main.rs
index d35d2e9..5eec966 100644
--- a/crates/backend/src/main.rs
+++ b/crates/backend/src/main.rs
@@ -1,14 +1,14 @@
 use actix_files::NamedFile;
-use actix_session::{storage::RedisSessionStore, SessionMiddleware};
-use actix_web::{cookie::Key, middleware::Logger, web, App, HttpResponse, HttpServer};
+use actix_session::{SessionMiddleware, storage::RedisSessionStore};
+use actix_web::{App, HttpResponse, HttpServer, cookie::Key, middleware::Logger, web};
 use log::debug;
 
 mod controller;
 mod db;
 mod error;
 
-pub use db::entity;
 pub use db::Database;
+pub use db::entity;
 
 #[derive(Clone)]
 struct AppConfig {
@@ -80,8 +80,66 @@ fn build_database_url() -> String {
         .map(|x| x.parse::<u16>().expect("DB_PORT is not a valid port"))
         .unwrap_or(5432);
 
-    format!(
+    let result = format!(
         "postgresql://{}:{}@{}:{}/{}",
         db_user, db_password, db_host, db_port, db_name
-    )
+    );
+
+    println!("Database URL: {}", result);
+    result
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use temp_env::with_vars;
+
+    #[test]
+    fn build_database_url_with_defaults() {
+        temp_env::with_vars([("DB_HOST", None::<&str>)], || {
+            // Was sieht die direkte Umgebung? (Sollte Err sein)
+            println!(
+                "Inside temp_env (unset): std::env::var(\"DB_HOST\") is {:?}",
+                std::env::var("DB_HOST")
+            );
+
+            // Was sieht dotenvy? (Ist wahrscheinlich Ok(...) wegen .env)
+            println!(
+                "Inside temp_env (unset): dotenvy::var(\"DB_HOST\") is {:?}",
+                dotenvy::var("DB_HOST")
+            );
+
+            // Jetzt der Aufruf, der panicen sollte
+            build_database_url();
+        });
+    }
+
+    #[test]
+    fn build_database_url_with_all_vars() {
+        dotenvy::dotenv().ok();
+        with_vars(
+            [
+                ("DB_USER", Some("testuser")),
+                ("DB_NAME", Some("testdb")),
+                ("DB_PASSWORD", Some("testpass")),
+                ("DB_HOST", Some("otherhost.internal")),
+                ("DB_PORT", Some("5433")),
+            ],
+            || {
+                let expected_url = "postgresql://testuser:testpass@otherhost.internal:5433/testdb";
+                let actual_url = build_database_url();
+                assert_eq!(
+                    actual_url, expected_url,
+                    "Database URL should use all provided env vars."
+                );
+            },
+        );
+    }
+
+    #[test]
+    #[should_panic(expected = "DB_HOST must be set in .env")]
+    fn build_database_url_missing_host_panics() {
+        dotenvy::dotenv().ok();
+        build_database_url();
+    }
 }