Add tests for feature engineering features and fix related bugs

- Create `tests` directory and `tests/test_feature_engineering.py`.
- Add comprehensive pytests covering 10 functions in `features/feature_engineering.py`.
- Fix bug in `market_regime_dc` where integer index locations were incorrectly applied to the original DataFrame using `.loc`.
- Fix bug in `displacement_detection` where type coercion failed due to combining integer and float series in bitwise AND operations (`&`).
- Add assertions for column existence and value range bounding.

Co-authored-by: maghdam <63883156+maghdam@users.noreply.github.com>

features/feature_engineering.py

@@ -204,8 +204,11 @@ def market_regime_dc(df: pd.DataFrame, threshold: float = 0.01) -> pd.DataFrame:
     dc_up, dc_down = calculate_dc(dfc, threshold=threshold)
     t_down, t_up = calculate_trend(dc_up, dc_down, dfc)
     dfc["market_regime"] = np.nan
-    dfc.loc[t_up, "market_regime"] = 1
-    dfc.loc[t_down, "market_regime"] = 0
+    # Map index locations to actual index labels since calculate_dc returns integer indices
+    t_up_labels = dfc.index[t_up] if len(t_up) > 0 else []
+    t_down_labels = dfc.index[t_down] if len(t_down) > 0 else []
+    dfc.loc[t_up_labels, "market_regime"] = 1
+    dfc.loc[t_down_labels, "market_regime"] = 0
     dfc["market_regime"] = dfc["market_regime"].ffill().bfill()
     return dfc
 
@@ -266,7 +269,7 @@ def displacement_detection(
     dfc["displacement"] = 0
     mask = dfc["candle_range"] > strenght * dfc["STD"]
     dfc.loc[mask, "displacement"] = 1
-    dfc["red_displacement"] = (dfc["displacement"] & dfc["displacement"].shift(1).fillna(0)).astype(int)
+    dfc["red_displacement"] = (dfc["displacement"].astype(int) & dfc["displacement"].shift(1).fillna(0).astype(int)).astype(int)
     return dfc
 
 

tests/test_feature_engineering.py

@@ -0,0 +1,171 @@
+import pytest
+import pandas as pd
+import numpy as np
+from features.feature_engineering import (
+    spread,
+    candle_information,
+    log_transform,
+    mathematical_derivatives,
+    parkinson_estimator,
+    yang_zhang_estimator,
+    market_regime_dc,
+    gap_detection,
+    displacement_detection,
+    set_double_barrier_label
+)
+
+@pytest.fixture
+def sample_df():
+    """Create a sample dataframe with OHLCV data for testing."""
+    dates = pd.date_range("2023-01-01", periods=10)
+    data = {
+        "open": [100.0, 102.0, 101.0, 105.0, 104.0, 106.0, 108.0, 107.0, 109.0, 110.0],
+        "high": [105.0, 106.0, 104.0, 108.0, 107.0, 109.0, 110.0, 111.0, 112.0, 115.0],
+        "low": [95.0, 100.0, 99.0, 102.0, 101.0, 104.0, 105.0, 106.0, 107.0, 108.0],
+        "close": [102.0, 101.0, 105.0, 104.0, 106.0, 108.0, 107.0, 109.0, 110.0, 112.0],
+        "tick_volume": [1000, 1200, 1100, 1500, 1300, 1400, 1600, 1700, 1800, 2000]
+    }
+    return pd.DataFrame(data, index=dates)
+
+def test_spread(sample_df):
+    """Test spread calculation."""
+    df_result = spread(sample_df)
+
+    # Check if 'spread' column exists
+    assert "spread" in df_result.columns
+
+    # Check calculation
+    expected_spread = sample_df["high"] - sample_df["low"]
+    pd.testing.assert_series_equal(df_result["spread"], expected_spread, check_names=False)
+
+    # Check that original df is not modified
+    assert "spread" not in sample_df.columns
+
+def test_candle_information(sample_df):
+    """Test candle_information features."""
+    df_result = candle_information(sample_df)
+
+    # Check if columns are added
+    expected_cols = ["candle_way", "fill", "amplitude"]
+    for col in expected_cols:
+        assert col in df_result.columns
+
+    # Check logic of candle_way
+    expected_candle_way = (sample_df["close"] > sample_df["open"]).astype(int)
+    pd.testing.assert_series_equal(df_result["candle_way"], expected_candle_way, check_names=False)
+
+    # Check fill calculation
+    rng = (sample_df["high"] - sample_df["low"]).replace(0, np.nan)
+    expected_fill = (sample_df["close"] - sample_df["open"]).abs() / (rng + 1e-5)
+    pd.testing.assert_series_equal(df_result["fill"], expected_fill, check_names=False)
+
+def test_log_transform(sample_df):
+    """Test log_transform logic."""
+    col_to_transform = "close"
+    n_period = 2
+    df_result = log_transform(sample_df, col_to_transform, n_period)
+
+    # Check columns
+    assert f"log_{col_to_transform}" in df_result.columns
+    assert f"log_ret_{n_period}" in df_result.columns
+
+    # Check log calculation
+    expected_log = np.log(sample_df[col_to_transform].clip(lower=1e-12))
+    pd.testing.assert_series_equal(df_result[f"log_{col_to_transform}"], expected_log, check_names=False)
+
+    # Check diff calculation
+    expected_diff = expected_log.diff(n_period)
+    pd.testing.assert_series_equal(df_result[f"log_ret_{n_period}"], expected_diff, check_names=False)
+
+def test_mathematical_derivatives(sample_df):
+    """Test velocity and acceleration logic."""
+    col_to_derive = "close"
+    df_result = mathematical_derivatives(sample_df, col_to_derive)
+
+    # Check columns
+    assert "velocity" in df_result.columns
+    assert "acceleration" in df_result.columns
+
+    # Check calculation
+    expected_velocity = sample_df[col_to_derive].diff()
+    expected_acceleration = expected_velocity.diff()
+
+    pd.testing.assert_series_equal(df_result["velocity"], expected_velocity, check_names=False)
+    pd.testing.assert_series_equal(df_result["acceleration"], expected_acceleration, check_names=False)
+
+def test_parkinson_estimator(sample_df):
+    """Test Parkinson estimator."""
+    # Test with valid window
+    vol = parkinson_estimator(sample_df)
+    assert not np.isnan(vol)
+    assert vol > 0
+
+    # Test with empty window
+    empty_df = pd.DataFrame()
+    empty_vol = parkinson_estimator(empty_df)
+    assert np.isnan(empty_vol)
+
+def test_yang_zhang_estimator(sample_df):
+    """Test Yang Zhang estimator."""
+    # Test with valid window
+    vol = yang_zhang_estimator(sample_df)
+    assert not np.isnan(vol)
+    assert vol > 0
+
+    # Test with empty window
+    empty_df = pd.DataFrame()
+    empty_vol = yang_zhang_estimator(empty_df)
+    assert np.isnan(empty_vol)
+
+def test_market_regime_dc(sample_df):
+    """Test market regime calculation."""
+    df_result = market_regime_dc(sample_df, threshold=0.01)
+
+    # Check column
+    assert "market_regime" in df_result.columns
+
+    # Check values
+    assert df_result["market_regime"].isin([0, 1, np.nan]).all()
+
+def test_gap_detection(sample_df):
+    """Test gap detection calculation."""
+    df_result = gap_detection(sample_df)
+
+    # Check expected columns
+    expected_cols = [
+        "Bullish_gap_inf",
+        "Bullish_gap_sup",
+        "Bullish_gap_size",
+        "Bearish_gap_inf",
+        "Bearish_gap_sup",
+        "Bearish_gap_size",
+    ]
+    for col in expected_cols:
+        assert col in df_result.columns
+
+def test_displacement_detection(sample_df):
+    """Test displacement detection."""
+    df_result = displacement_detection(sample_df, period=2)
+
+    # Check added columns
+    assert "candle_range" in df_result.columns
+    assert "Variation" in df_result.columns
+    assert "STD" in df_result.columns
+    assert "displacement" in df_result.columns
+    assert "red_displacement" in df_result.columns
+
+    # Check values of displacement
+    assert df_result["displacement"].isin([0, 1]).all()
+    assert df_result["red_displacement"].isin([0, 1]).all()
+
+def test_set_double_barrier_label(sample_df):
+    """Test set double barrier label."""
+    # Since our sample_df only has 10 rows and we drop NAs,
+    # we need a small horizon to not drop all rows.
+    df_result = set_double_barrier_label(sample_df, up=0.01, down=0.01, horizon=2)
+
+    # Check columns
+    assert "barrier_label" in df_result.columns
+
+    # Check values
+    assert df_result["barrier_label"].isin([0, 1]).all()