feat(api): Making WeaviateClient a singleton

Co-authored-by: lijiezhao <lijiezhao@perfect99.com>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

api/tests/unit_tests/core/rag/datasource/vdb/weaviate/test_weavaite.py

@@ -0,0 +1,33 @@
+from unittest.mock import MagicMock, patch
+
+from core.rag.datasource.vdb.weaviate.weaviate_vector import WeaviateConfig, WeaviateVector
+
+
+def test_init_client_with_valid_config():
+    """Test successful client initialization with valid configuration."""
+    config = WeaviateConfig(
+        endpoint="http://localhost:8080",
+        api_key="WVF5YThaHlkYwhGUSmCRgsX3tD5ngdN8pkih",
+    )
+
+    with patch("weaviate.connect_to_custom") as mock_connect:
+        mock_client = MagicMock()
+        mock_client.is_ready.return_value = True
+        mock_connect.return_value = mock_client
+
+        vector = WeaviateVector(
+            collection_name="test_collection",
+            config=config,
+            attributes=["doc_id"],
+        )
+
+        assert vector._client == mock_client
+        mock_connect.assert_called_once()
+        call_kwargs = mock_connect.call_args[1]
+        assert call_kwargs["http_host"] == "localhost"
+        assert call_kwargs["http_port"] == 8080
+        assert call_kwargs["http_secure"] is False
+        assert call_kwargs["grpc_host"] == "localhost"
+        assert call_kwargs["grpc_port"] == 50051
+        assert call_kwargs["grpc_secure"] is False
+        assert call_kwargs["auth_credentials"] is not None