test(gooddata-eval): cover multi-run reasoning_steps retention

Addresses CodeRabbit nitpick on PR #1708: a later run returning no
reasoning events must not clobber an earlier run's captured steps
(runner.py:120's `or` pattern, same as conversation_id/response_id).

Author: Tomkess

packages/gooddata-eval/tests/test_runner.py

@@ -277,6 +277,22 @@ def test_run_items_reasoning_steps_empty_when_chat_result_has_none():
     assert report.items[0].reasoning_steps == []
 
 
+def test_run_items_reasoning_steps_keeps_earlier_run_when_later_run_is_empty():
+    """A later run with no reasoning events must not clobber an earlier run's steps (runner.py:120's `or`)."""
+
+    class _MixedReasoningBackend:
+        def __init__(self):
+            self.calls = 0
+
+        def ask(self, item: DatasetItem) -> ChatResult:
+            self.calls += 1
+            steps = ["step one", "step two"] if self.calls == 1 else []
+            return ChatResult.model_validate({"textResponse": "answer", "reasoningSteps": steps})
+
+    report = run_items([_item()], _MixedReasoningBackend(), runs=2)
+    assert report.items[0].reasoning_steps == ["step one", "step two"]
+
+
 def test_run_items_callback_exception_is_logged_not_swallowed(capsys):
     """A raising callback prints a traceback to stderr but the run continues."""
     backend = _FakeBackend([_chat_with(_viz_obj())] * 2)