test(python): verify FTS build controls

python/src/index.rs

@@ -452,3 +452,51 @@ impl IndexConfig {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use pyo3::types::{PyDict, PyDictMethods};
+    use serde_json::json;
+
+    #[test]
+    fn fts_build_controls_are_forwarded() {
+        Python::initialize();
+        Python::attach(|py| {
+            let locals = PyDict::new(py);
+            py.run(
+                c"class FTS:
+    with_position = True
+    base_tokenizer = 'simple'
+    language = 'English'
+    max_token_length = None
+    lower_case = True
+    stem = False
+    remove_stop_words = False
+    custom_stop_words = None
+    ascii_folding = False
+    ngram_min_length = 3
+    ngram_max_length = 3
+    prefix_only = False
+    block_size = 128
+    memory_limit = 2048
+    num_workers = 7
+
+config = FTS()",
+                None,
+                Some(&locals),
+            )
+            .unwrap();
+
+            let config = locals.get_item("config").unwrap().unwrap();
+            let index = extract_index_params(&Some(config)).unwrap();
+            let LanceDbIndex::FTS(params) = index else {
+                panic!("expected FTS index parameters");
+            };
+            let training_json = params.to_training_json().unwrap();
+
+            assert_eq!(training_json.get("memory_limit"), Some(&json!(2048)));
+            assert_eq!(training_json.get("num_workers"), Some(&json!(7)));
+        });
+    }
+}