Test: Add tests for path handling in rd() function

- Test absolute filename with data_path (main bug fix scenario)
- Test relative filename with data_path
- Test missing XML sidecar error handling
- Added pytest as dev dependency

2 files changed, 130 insertions, 0 deletions

diff --git a/pyproject.toml b/pyproject.toml
index 859c39e..9f01784 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -22,3 +22,8 @@ build-backend = "setuptools.build_meta"
 [tool.setuptools.packages.find]
 where = ["src"]
 
+[dependency-groups]
+dev = [
+    "pytest>=8.3.5",
+]
+
diff --git a/tests/test_io_path_handling.py b/tests/test_io_path_handling.py
new file mode 100644
index 0000000..8c140ca
--- /dev/null
+++ b/tests/test_io_path_handling.py
@@ -0,0 +1,125 @@
+"""Test path handling in io.py, particularly for rd() function."""
+
+import os
+import tempfile
+from pathlib import Path
+
+import numpy as np
+import pytest
+
+from transivent.io import get_waveform_params, rd
+
+
+def test_rd_with_data_path_and_absolute_filename():
+    """
+    Test that rd() correctly handles data_path when filename is absolute.
+    
+    This tests the fix for the issue where rd() would ignore data_path
+    if filename was an absolute path, causing XML sidecar lookup to fail.
+    """
+    with tempfile.TemporaryDirectory() as tmpdir:
+        # Create test data directory
+        data_dir = Path(tmpdir) / "data"
+        data_dir.mkdir()
+        
+        # Create test files
+        bin_file = data_dir / "test.Wfm.bin"
+        xml_file = data_dir / "test.bin"
+        
+        # Create a simple binary file with header
+        # Header: 8 bytes (element_size=4, record_length=1000)
+        # Data: 1000 float32 values
+        header = np.array([4, 1000], dtype=np.uint32)
+        data = np.random.randn(1000).astype(np.float32)
+        
+        with open(bin_file, "wb") as f:
+            header.tofile(f)
+            data.tofile(f)
+        
+        # Create XML sidecar content
+        xml_content = """<?xml version="1.0" standalone="no"?>
+<Database>
+    <Group Name="ReferenceCurveAttributes">
+        <Prop Name="Resolution" Value="5e-08"/>
+        <Prop Name="ByteOrder" Value="LSB"/>
+        <Prop Name="SignalFormat" Value="FLOAT"/>
+        <Prop Name="SignalHardwareRecordLength" Value="1000"/>
+    </Group>
+</Database>"""
+        
+        with open(xml_file, "w") as f:
+            f.write(xml_content)
+        
+        # Test 1: rd() with absolute filename and data_path should work
+        # This is the main test for the fix
+        time, signal = rd(str(bin_file.absolute()), data_path=str(data_dir))
+        
+        assert len(time) == 1000
+        assert len(signal) == 1000
+        assert time[1] - time[0] == 5e-08
+        
+        # Test 2: rd() with relative filename and data_path should also work
+        os.chdir(tmpdir)
+        time2, signal2 = rd("test.Wfm.bin", data_path="data")
+        
+        np.testing.assert_array_equal(time, time2)
+        np.testing.assert_array_equal(signal, signal2)
+        
+        # Test 3: rd() without data_path should work if XML is in same dir
+        time3, signal3 = rd(str(bin_file))
+        
+        np.testing.assert_array_equal(time, time3)
+        np.testing.assert_array_equal(signal, signal3)
+
+
+def test_get_waveform_params_with_data_path():
+    """Test that get_waveform_params correctly uses data_path."""
+    with tempfile.TemporaryDirectory() as tmpdir:
+        # Create test XML file
+        xml_file = Path(tmpdir) / "test.bin"
+        xml_content = """<?xml version="1.0" standalone="no"?>
+<Database>
+    <Group Name="ReferenceCurveAttributes">
+        <Prop Name="Resolution" Value="1e-07"/>
+        <Prop Name="ByteOrder" Value="MSB"/>
+        <Prop Name="SignalFormat" Value="INT16"/>
+    </Group>
+</Database>"""
+        
+        with open(xml_file, "w") as f:
+            f.write(xml_content)
+        
+        # Test with data_path
+        params = get_waveform_params("test.Wfm.bin", data_path=tmpdir)
+        
+        assert params["sampling_interval"] == 1e-07
+        assert params["byte_order"] == "MSB"
+        assert params["signal_format"] == "int16"
+
+
+def test_rd_missing_xml_sidecar():
+    """Test that rd() raises appropriate error when XML sidecar is missing."""
+    with tempfile.TemporaryDirectory() as tmpdir:
+        # Create only binary file, no XML
+        bin_file = Path(tmpdir) / "test.Wfm.bin"
+        header = np.array([4, 1000], dtype=np.uint32)
+        data = np.random.randn(1000).astype(np.float32)
+        
+        with open(bin_file, "wb") as f:
+            header.tofile(f)
+            data.tofile(f)
+        
+        # Should raise FileNotFoundError for missing XML
+        with pytest.raises(FileNotFoundError, match="XML sidecar file not found"):
+            rd(str(bin_file), data_path=tmpdir)
+        
+        # Also should fail without data_path
+        with pytest.raises(FileNotFoundError, match="XML sidecar file not found"):
+            rd(str(bin_file))
+
+
+if __name__ == "__main__":
+    test_rd_with_data_path_and_absolute_filename()
+    test_get_waveform_params_with_data_path()
+    test_rd_missing_xml_sidecar()
+    print("All tests passed!")
\ No newline at end of file