Added test

tests/overview_tests.rs

@@ -0,0 +1,13 @@
+use rabbitmq_http_client::blocking::Client;
+
+mod common;
+use crate::common::{endpoint, PASSWORD, USERNAME};
+
+#[test]
+fn test_overview() {
+    let endpoint = endpoint();
+    let rc = Client::new(&endpoint, USERNAME, PASSWORD);
+
+    let result1 = rc.overview();
+    assert!(result1.is_ok(), "overview returned {:?}", result1);
+}