Remove superfluous DummyFile test

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: msch-nutrient

tests/unit/test_file_handler.py

@@ -42,15 +42,3 @@ def test_get_file_size_from_bytesio():
     file_obj = io.BytesIO(content)
     size = get_file_size(file_obj)
     assert size == 12
-
-
-def test_get_file_size_none():
-    """Test get_file_size returns None for invalid input."""
-    from nutrient_dws.file_handler import get_file_size
-
-    # Test with a file-like object without proper methods
-    class DummyFile:
-        pass
-
-    size = get_file_size(DummyFile())  # type: ignore[arg-type]
-    assert size is None