diff --git a/tests/server.rs b/tests/server.rs
index d77a562..b1554ea 100644
--- a/tests/server.rs
+++ b/tests/server.rs
@@ -31,6 +31,15 @@ fn test_new_server_invalid_key() {
     let _ = MetricsServer::new("localhost:8442", Some(cert), Some(key));
 }
 
+#[test]
+#[should_panic]
+fn test_new_server_already_running() {
+    let srv = MetricsServer::new("localhost:8002", None, None).serve();
+
+    // Attempt to start an already running server.
+    srv.serve();
+}
+
 #[test]
 fn test_new_https_server() {
     // Load TLS config.