Add bad_request error tests

meilisearch-http/tests/index/stats.rs

@@ -46,3 +46,19 @@ async fn stats() {
     assert_eq!(response["fieldDistribution"]["name"], 1);
     assert_eq!(response["fieldDistribution"]["age"], 1);
 }
+
+#[actix_rt::test]
+async fn error_get_stats_unexisting_index() {
+    let server = Server::new().await;
+    let (response, code) = server.index("test").stats().await;
+
+    let expected_response = json!({
+        "message": "Index test not found.",
+        "code": "index_not_found",
+        "type": "invalid_request",
+        "link": "https://docs.meilisearch.com/errors#index_not_found"
+    });
+
+    assert_eq!(response, expected_response);
+    assert_eq!(code, 404);
+}