fix: merge backtest config over DEFAULT_CONFIG so empty overrides work

Author: zkwang616

tests/test_backtest_harness.py

@@ -134,6 +134,29 @@ def fake_factory(config):
     assert captured["config"]["memory_log_path"] is None
 
 
+@pytest.mark.unit
+def test_run_backtest_merges_defaults_when_config_is_empty_dict(monkeypatch):
+    # Regression: the CLI passes config={} when no provider/model flags are
+    # given; run_backtest must fall back to DEFAULT_CONFIG for every other key
+    # instead of handing TradingAgentsGraph a one-key dict (#1234).
+    captured = {}
+
+    def fake_factory(config):
+        captured["config"] = config
+        return _FakeGraph(config)
+
+    monkeypatch.setattr(backtest, "TradingAgentsGraph", fake_factory)
+    df, _ = backtest.run_backtest(
+        tickers=["NVDA"],
+        dates=["2024-01-01"],
+        config={},
+    )
+    assert len(df) == 1
+    assert captured["config"]["data_cache_dir"]
+    assert captured["config"]["llm_provider"]
+    assert captured["config"]["memory_log_path"] is None
+
+
 @pytest.mark.unit
 def test_run_backtest_records_failures_and_continues(monkeypatch):
     monkeypatch.setattr(backtest, "TradingAgentsGraph", _FlakyGraph)

tradingagents/evaluation/backtest.py

@@ -77,12 +77,12 @@ def run_backtest(
     Returns:
         ``(results_df, markdown_summary)``.
     """
-    if config is None:
-        cfg = DEFAULT_CONFIG.copy()
-        cfg["memory_log_path"] = None
-    else:
-        cfg = dict(config)
-        cfg.setdefault("memory_log_path", None)
+    cfg = DEFAULT_CONFIG.copy()
+    if config:
+        cfg.update(config)
+    # Backtests stay out of the persistent decision log unless the caller
+    # explicitly opts in with a memory_log_path of their own.
+    cfg["memory_log_path"] = (config or {}).get("memory_log_path")
 
     graph = TradingAgentsGraph(config=cfg)
     rows: list[dict] = []