diff --git a/tests/unit/test_stockstats_utils.py b/tests/unit/test_stockstats_utils.py
index 0009bf07..3f1ede01 100644
--- a/tests/unit/test_stockstats_utils.py
+++ b/tests/unit/test_stockstats_utils.py
@@ -1,22 +1,153 @@
 import pandas as pd
+import numpy as np
+import pytest
 from tradingagents.dataflows.stockstats_utils import _clean_dataframe
 
-def test_clean_dataframe_lowercases_columns():
+def test_clean_dataframe_valid_data():
+    """Test _clean_dataframe with valid data where no rows should be dropped."""
     df = pd.DataFrame({
         "Date": ["2023-01-01", "2023-01-02", "2023-01-03"],
         "Open": [10.0, 11.0, 12.0],
-        "HIGH": [10.5, 11.5, 12.5],
-        "low": [9.5, 10.5, 11.5],
-        "ClOsE": [10.2, 11.2, 12.2],
-        "Volume": [1000, 1100, 1200]
+        "High": [10.5, 11.5, 12.5],
+        "Low": [9.5, 10.5, 11.5],
+        "Close": [10.2, 11.2, 12.2],
+        "Volume": [100, 200, 300]
     })
 
-    cleaned = _clean_dataframe(df)
+    cleaned_df = _clean_dataframe(df.copy())
 
-    assert list(cleaned.columns) == ["date", "open", "high", "low", "close", "volume"]
-    assert len(cleaned) == 3
+    assert len(cleaned_df) == 3
+    assert "date" in cleaned_df.columns
+    assert pd.api.types.is_datetime64_any_dtype(cleaned_df["date"])
 
-def test_clean_dataframe_handles_non_string_columns():
+    # Check if price columns are correctly parsed as float/numeric
+    for col in ["open", "high", "low", "close", "volume"]:
+        assert pd.api.types.is_numeric_dtype(cleaned_df[col])
+        assert (cleaned_df[col] == df[col.capitalize()]).all()
+
+def test_clean_dataframe_invalid_dates():
+    """Test _clean_dataframe drops rows with invalid or missing dates."""
+    df = pd.DataFrame({
+        "Date": ["2023-01-01", "invalid_date", None],
+        "Open": [10.0, 11.0, 12.0],
+        "Close": [10.2, 11.2, 12.2]
+    })
+
+    cleaned_df = _clean_dataframe(df.copy())
+
+    assert len(cleaned_df) == 1
+    assert cleaned_df.iloc[0]["date"] == pd.to_datetime("2023-01-01")
+
+def test_clean_dataframe_missing_close():
+    """Test _clean_dataframe drops rows where Close price is missing."""
+    df = pd.DataFrame({
+        "Date": ["2023-01-01", "2023-01-02", "2023-01-03"],
+        "Open": [10.0, 11.0, 12.0],
+        "Close": [10.2, np.nan, 12.2]
+    })
+
+    cleaned_df = _clean_dataframe(df.copy())
+
+    assert len(cleaned_df) == 2
+    assert cleaned_df.iloc[0]["date"] == pd.to_datetime("2023-01-01")
+    assert cleaned_df.iloc[1]["date"] == pd.to_datetime("2023-01-03")
+
+def test_clean_dataframe_numeric_coercion():
+    """Test _clean_dataframe coerces non-numeric strings to NaN in price columns,
+    but handles ffill/bfill for them."""
+    df = pd.DataFrame({
+        "Date": ["2023-01-01", "2023-01-02", "2023-01-03", "2023-01-04"],
+        "Open": [10.0, "invalid", 12.0, 13.0],
+        "Close": [10.2, 11.2, 12.2, 13.2]
+    })
+
+    cleaned_df = _clean_dataframe(df.copy())
+
+    assert len(cleaned_df) == 4
+    # "invalid" is coerced to NaN, then ffill will fill it with 10.0 (from previous row)
+    assert cleaned_df.iloc[1]["open"] == 10.0
+
+def test_clean_dataframe_ffill_bfill():
+    """Test _clean_dataframe forward and backward fills missing values in price columns."""
+    df = pd.DataFrame({
+        "Date": ["2023-01-01", "2023-01-02", "2023-01-03"],
+        "Open": [np.nan, 11.0, np.nan],
+        "Close": [10.2, 11.2, 12.2]
+    })
+
+    cleaned_df = _clean_dataframe(df.copy())
+
+    assert len(cleaned_df) == 3
+    # The first row Open is NaN -> bfill uses the next valid value (11.0)
+    assert cleaned_df.iloc[0]["open"] == 11.0
+    # The last row Open is NaN -> ffill uses the previous valid value (11.0)
+    assert cleaned_df.iloc[2]["open"] == 11.0
+
+def test_clean_dataframe_empty():
+    """Test _clean_dataframe with an empty DataFrame."""
+    df = pd.DataFrame(columns=["Date", "Open", "Close"])
+
+    cleaned_df = _clean_dataframe(df.copy())
+
+    assert len(cleaned_df) == 0
+    assert "date" in cleaned_df.columns
+    assert "open" in cleaned_df.columns
+    assert "close" in cleaned_df.columns
+
+def test_clean_dataframe_missing_columns():
+    """Test _clean_dataframe when some optional price columns are missing."""
+    df = pd.DataFrame({
+        "Date": ["2023-01-01", "2023-01-02"],
+        "Close": [10.2, 11.2]
+    })
+
+    cleaned_df = _clean_dataframe(df.copy())
+
+    assert len(cleaned_df) == 2
+    assert "close" in cleaned_df.columns
+    assert "open" not in cleaned_df.columns
+
+def test_clean_dataframe_lowercase_columns():
+    """Test _clean_dataframe successfully lowercases all column names."""
+    # Given a DataFrame with mixed case and uppercase columns
+    df = pd.DataFrame({
+        "Date": ["2023-01-01"],
+        "OPEN": [10.0],
+        "High": [10.5],
+        "loW": [9.5],
+        "Close": [10.2],
+        "Volume": [100]
+    })
+
+    # When _clean_dataframe is called
+    cleaned_df = _clean_dataframe(df)
+
+    # Then all columns should be lowercase
+    expected_columns = ["date", "open", "high", "low", "close", "volume"]
+    assert list(cleaned_df.columns) == expected_columns
+
+    # And the original DataFrame should not be mutated
+    assert list(df.columns) == ["Date", "OPEN", "High", "loW", "Close", "Volume"]
+
+def test_clean_dataframe_non_string_columns():
+    """Test _clean_dataframe successfully handles non-string column names by converting them to string then lowercase."""
+    # Given a DataFrame with integer columns (which won't match Date or Close processing but will be lowercased)
+    df = pd.DataFrame({
+        "Date": ["2023-01-01"],
+        "Close": [10.0],
+        0: [100.0],
+        1: [200.0]
+    })
+
+    # When _clean_dataframe is called
+    cleaned_df = _clean_dataframe(df)
+
+    # Then all columns should be strings and lowercase
+    expected_columns = ["date", "close", "0", "1"]
+    assert list(cleaned_df.columns) == expected_columns
+
+def test_clean_dataframe_handles_no_date_or_close():
+    """Test _clean_dataframe correctly formats column names if there's no date or close"""
     df = pd.DataFrame({
         1: [10.0, 11.0],
         "Open": [10.0, 11.0]
@@ -25,13 +156,4 @@ def test_clean_dataframe_handles_non_string_columns():
     cleaned = _clean_dataframe(df)
 
     assert list(cleaned.columns) == ["1", "open"]
-
-def test_clean_dataframe_does_not_mutate_original():
-    df = pd.DataFrame({
-        "Date": ["2023-01-01", "2023-01-02", "2023-01-03"],
-        "Open": [10.0, 11.0, 12.0]
-    })
-
-    _clean_dataframe(df)
-
-    assert list(df.columns) == ["Date", "Open"]
+    assert len(cleaned) == 2
diff --git a/tests/unit/test_ttm_analysis.py b/tests/unit/test_ttm_analysis.py
index 2cdede41..5dc0957a 100644
--- a/tests/unit/test_ttm_analysis.py
+++ b/tests/unit/test_ttm_analysis.py
@@ -60,15 +60,21 @@ class TestFindCol:
         from tradingagents.dataflows.ttm_analysis import _find_col
         self.find_col = _find_col
 
-    def test_find_col_success(self):
-        df = pd.DataFrame({"Total Revenue": [100], "Gross Profit": [40]})
-        candidates = ["Revenue", "Total Revenue", "totalRevenue"]
-        assert self.find_col(df, candidates) == "Total Revenue"
+    def test_find_col_match(self):
+        """Should return the matching column name."""
+        df = pd.DataFrame({"Revenue": [1, 2, 3], "Cost": [4, 5, 6]})
+        assert self.find_col(df, ["Revenue", "Total Revenue"]) == "Revenue"
+
+    def test_find_col_no_match(self):
+        """Should return None if no candidate matches."""
+        df = pd.DataFrame({"Cost": [4, 5, 6], "Profit": [7, 8, 9]})
+        assert self.find_col(df, ["Revenue", "Total Revenue"]) is None
+
+    def test_find_col_empty_df(self):
+        """Should return None for empty DataFrame."""
+        df = pd.DataFrame()
+        assert self.find_col(df, ["Revenue", "Total Revenue"]) is None
 
-    def test_find_col_not_found(self):
-        df = pd.DataFrame({"Unrelated": [100], "Another": [40]})
-        candidates = ["Revenue", "Total Revenue", "totalRevenue"]
-        assert self.find_col(df, candidates) is None
 
 # ---------------------------------------------------------------------------
 # Unit tests for compute_ttm_metrics
diff --git a/tradingagents/dataflows/stockstats_utils.py b/tradingagents/dataflows/stockstats_utils.py
index ee0875b9..9d43cf0e 100644
--- a/tradingagents/dataflows/stockstats_utils.py
+++ b/tradingagents/dataflows/stockstats_utils.py
@@ -7,9 +7,25 @@ from .config import get_config
 
 
 def _clean_dataframe(data: pd.DataFrame) -> pd.DataFrame:
-    """Ensure DataFrame has lowercase columns for stockstats."""
+    """Normalize a stock DataFrame for stockstats: parse dates, drop invalid rows, fill price gaps.
+    Ensure DataFrame has lowercase columns for stockstats."""
     df = data.copy()
     df.columns = [str(c).lower() for c in df.columns]
+
+    if "date" in df.columns:
+        df["date"] = pd.to_datetime(df["date"], errors="coerce")
+        df = df.dropna(subset=["date"])
+
+    price_cols = [c for c in ["open", "high", "low", "close", "volume"] if c in df.columns]
+    if price_cols:
+        df[price_cols] = df[price_cols].apply(pd.to_numeric, errors="coerce")
+
+    if "close" in df.columns:
+        df = df.dropna(subset=["close"])
+
+    if price_cols:
+        df[price_cols] = df[price_cols].ffill().bfill()
+
     return df