Establish automated test foundation

tests/test_library.py

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+from pathlib import Path
+
+from serato_doctor.models.library import Library
+from serato_doctor.models.reference import TrackReference
+from serato_doctor.models.track import DiskTrack
+
+
+def test_library_reconciles_references_by_filename():
+    crate = Path("House.crate")
+    references = [
+        TrackReference(crate, Path("/old/Found.mp3"), "Found.mp3"),
+        TrackReference(crate, Path("/old/Missing.mp3"), "Missing.mp3"),
+    ]
+    tracks = [DiskTrack(Path("/new/Found.mp3"), "Found.mp3", 10, ".mp3")]
+
+    results = Library.build(references, tracks).reconcile_by_filename()
+
+    assert [result.exists_by_filename for result in results] == [True, False]
+    assert results[1].as_row() == {
+        "crate": "House.crate",
+        "serato_path": "/old/Missing.mp3",
+        "filename": "Missing.mp3",
+        "exists_by_filename": False,
+    }