Fix string representation for load params with empty fields

Signed-off-by: Andrey Berezin <a.berezin@yadro.com>

tests/test_load_config.py

@@ -3,7 +3,17 @@ from typing import Any, get_args
 
 import pytest
 
-from frostfs_testlib.load.load_config import LoadParams, LoadScenario, LoadType, Preset
+from frostfs_testlib.load.load_config import (
+    EndpointSelectionStrategy,
+    LoadParams,
+    LoadScenario,
+    LoadType,
+    Preset,
+)
+from frostfs_testlib.storage.cluster import ClusterNode
+from frostfs_testlib.storage.controllers.background_load_controller import BackgroundLoadController
+from frostfs_testlib.storage.dataclasses.frostfs_services import StorageNode
+from frostfs_testlib.storage.dataclasses.node_base import NodeBase
 
 
 @dataclass
@@ -36,7 +46,10 @@ class TestLoadConfig:
         return self._get_filled_load_params(load_type, load_scenario, set_empty)
 
     def test_load_params_only_load_type_required(self):
-        LoadParams(load_type=LoadType.S3)
+        load_params = LoadParams(load_type=LoadType.S3)
+        expected = "load: s3"
+        assert repr(load_params) == expected
+        assert f"{load_params}" == expected
 
     def test_load_params_initially_have_all_values_none(self):
         load_params = LoadParams(load_type=LoadType.S3)
@@ -60,6 +73,17 @@ class TestLoadConfig:
         assert f"{load_params}" == expected
         assert repr(load_params) == expected
 
+    @pytest.mark.parametrize("load_params", [LoadScenario.gRPC], indirect=True)
+    def test_load_controller_string_representation(self, load_params: LoadParams):
+        load_params.endpoint_selection_strategy = EndpointSelectionStrategy.ALL
+        load_params.object_size = 512
+        background_load_controller = BackgroundLoadController(
+            "tmp", load_params, "wallet", None, None
+        )
+        expected = "load: grpc (512 KiB), writers=7, readers=7, deleters=8"
+        assert f"{background_load_controller}" == expected
+        assert repr(background_load_controller) == expected
+
     def test_load_set_id_changes_fields(self):
         load_params = LoadParams(load_type=LoadType.S3)
         load_params.preset = Preset()