Add test file for data/data_loader.py

This commit introduces a new test file, `tests/test_data_loader.py`, to verify the functionality of `get_data_mt5`. It uses `unittest.mock.MagicMock` to mock the `MetaTrader5` module, allowing tests to run on Linux where the module cannot be imported.

The tests cover:
- Live trading data retrieval (`start_pos=None`).
- Backtesting data retrieval with a specific `start_pos`.
- Error handling when `copy_rates_from_pos` returns `None`.
- The proper conversion of rates into a pandas DataFrame with a parsed datetime index.

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

tests/test_data_loader.py

@@ -0,0 +1,74 @@
+import sys
+from unittest.mock import MagicMock
+
+# Mock MetaTrader5 before importing data_loader
+mt5_mock = MagicMock()
+sys.modules['MetaTrader5'] = mt5_mock
+
+import pandas as pd
+import pytest
+from data.data_loader import get_data_mt5
+
+def test_get_data_mt5_live_trading():
+    """Test get_data_mt5 when start_pos is None (live trading)."""
+    # Arrange
+    symbol = "BTCUSD"
+    n_bars = 100
+    timeframe = mt5_mock.TIMEFRAME_H1
+
+    # Mock return value of copy_rates_from_pos
+    mock_rates = [
+        {"time": 1600000000, "open": 1.0, "high": 2.0, "low": 0.5, "close": 1.5},
+        {"time": 1600003600, "open": 1.5, "high": 2.5, "low": 1.0, "close": 2.0},
+    ]
+    mt5_mock.copy_rates_from_pos.return_value = mock_rates
+
+    # Act
+    df = get_data_mt5(symbol, n_bars, timeframe)
+
+    # Assert
+    mt5_mock.copy_rates_from_pos.assert_called_once_with(symbol, timeframe, 0, n_bars)
+    assert isinstance(df, pd.DataFrame)
+    assert df.index.name == 'time'
+    assert len(df) == 2
+    assert "open" in df.columns
+    assert df.index[0] == pd.to_datetime(1600000000, unit='s')
+
+def test_get_data_mt5_backtesting():
+    """Test get_data_mt5 when start_pos is provided (backtesting)."""
+    # Arrange
+    mt5_mock.copy_rates_from_pos.reset_mock()
+    symbol = "EURUSD"
+    n_bars = 50
+    timeframe = mt5_mock.TIMEFRAME_M15
+    start_pos = 10
+
+    mock_rates = [
+        {"time": 1600000000, "open": 1.1, "high": 1.2, "low": 1.0, "close": 1.15},
+    ]
+    mt5_mock.copy_rates_from_pos.return_value = mock_rates
+
+    # Act
+    df = get_data_mt5(symbol, n_bars, timeframe, start_pos=start_pos)
+
+    # Assert
+    mt5_mock.copy_rates_from_pos.assert_called_once_with(symbol, timeframe, start_pos, n_bars)
+    assert isinstance(df, pd.DataFrame)
+    assert df.index.name == 'time'
+    assert len(df) == 1
+
+def test_get_data_mt5_no_data():
+    """Test get_data_mt5 when copy_rates_from_pos returns None."""
+    # Arrange
+    mt5_mock.copy_rates_from_pos.reset_mock()
+    symbol = "INVALID"
+    n_bars = 10
+    timeframe = mt5_mock.TIMEFRAME_H1
+
+    mt5_mock.copy_rates_from_pos.return_value = None
+
+    # Act & Assert
+    with pytest.raises(ValueError, match=f"Could not retrieve data for {symbol}"):
+        get_data_mt5(symbol, n_bars, timeframe)
+
+    mt5_mock.copy_rates_from_pos.assert_called_once_with(symbol, timeframe, 0, n_bars)