Add unit tests for version handling in doubleml package

Author: SvenKlaassen

doubleml/tests/test_init.py

@@ -0,0 +1,38 @@
+import importlib
+import sys
+from unittest.mock import patch
+
+import pytest
+
+
+@pytest.mark.ci
+def test_version_from_version_file():
+    """Test version is imported from _version.py when available."""
+    import doubleml
+
+    assert hasattr(doubleml, "__version__")
+    assert isinstance(doubleml.__version__, str)
+
+
+@pytest.mark.ci
+def test_version_fallback_to_metadata():
+    """Test fallback to importlib.metadata when _version.py is missing."""
+    with patch.dict(sys.modules, {"doubleml._version": None}):
+        with patch("importlib.metadata.version", return_value="1.2.3"):
+            # Re-import to trigger the fallback
+            importlib.reload(importlib.import_module("doubleml"))
+            import doubleml
+
+            assert doubleml.__version__ == "1.2.3"
+
+
+@pytest.mark.ci
+def test_version_fallback_to_unknown():
+    """Test fallback to 0.0.0+unknown when package not found."""
+    mock_error = importlib.metadata.PackageNotFoundError()
+    with patch.dict(sys.modules, {"doubleml._version": None}):
+        with patch("importlib.metadata.version", side_effect=mock_error):
+            importlib.reload(importlib.import_module("doubleml"))
+            import doubleml
+
+            assert doubleml.__version__ == "0.0.0+unknown"