Add opt-in diagnostic logging

tests/test_cli.py

@@ -37,7 +37,9 @@ def test_cli_writes_reports_and_prints_counts(tmp_path, monkeypatch, capsys):
 
     main()
 
-    output = capsys.readouterr().out
+    captured = capsys.readouterr()
+    output = captured.out
+    assert captured.err == ""
     assert "Crate references: 2" in output
     assert "Disk tracks: 1" in output
     assert "Missing by filename: 1" in output

tests/test_logging.py

@@ -0,0 +1,34 @@
+import logging
+
+from serato_doctor.logging import LOGGER_NAME, configure_logging
+
+
+def test_logging_is_quiet_by_default(capsys):
+    logger = configure_logging()
+
+    logger.info("not visible")
+
+    assert capsys.readouterr().err == ""
+
+
+def test_logging_writes_aggregate_progress_to_file(tmp_path):
+    log_path = tmp_path / "scan.log"
+    logger = configure_logging(log_file=log_path)
+
+    logger.info("Scanned %d disk tracks", 10)
+
+    contents = log_path.read_text(encoding="utf-8")
+    assert "INFO Scanned 10 disk tracks" in contents
+
+
+def test_reconfiguring_logging_replaces_handlers():
+    configure_logging(verbose=True)
+    logger = configure_logging(verbose=True)
+
+    active_handlers = [
+        handler
+        for handler in logger.handlers
+        if not isinstance(handler, logging.NullHandler)
+    ]
+    assert logger.name == LOGGER_NAME
+    assert len(active_handlers) == 1