Fix and expand tests: 63 tests passing, covers all core modules

Remove tests/ from .gitignore (was accidentally excluded).

- test_ripper.py: rewrite for current API (_parse_cddb_lines,
  _extract_tracks, _rename_files, _clean_input); fix default quality
- test_organizer.py: update filename assertions (spaces→underscores);
  add TestSanitizeFilename, TestCheckDiscCounts, in-place mode
- test_playlist.py: fix dummy filenames to underscore scheme;
  add multi-disc, filename sanitization, EXTINF and fallback tests

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

tests/test_playlist.py

@@ -0,0 +1,98 @@
+"""Tests für die Playlist-Generierung."""
+
+from pathlib import Path
+
+from musiksammlung.models import Album, Disc, Track
+from musiksammlung.playlist import generate_playlist
+
+
+def _make_album(n_tracks: int = 2, n_discs: int = 1) -> Album:
+    discs = [
+        Disc(
+            disc_number=d,
+            tracks=[Track(track_number=i, title=f"Disc{d} Song {i}") for i in range(1, n_tracks + 1)],
+        )
+        for d in range(1, n_discs + 1)
+    ]
+    return Album(artist="Artist", album="TestAlbum", year=2000, discs=discs)
+
+
+def test_generate_playlist_single_disc(tmp_path: Path):
+    """M3U für Single-CD: keine CD-Prefix, korrekte Dateinamen."""
+    album = _make_album(n_tracks=2, n_discs=1)
+
+    # Dummy-Audiodateien im neuen Unterstrich-Schema
+    (tmp_path / "01_Disc1_Song_1.flac").touch()
+    (tmp_path / "02_Disc1_Song_2.flac").touch()
+
+    playlist_path = generate_playlist(album, tmp_path)
+    assert playlist_path.exists()
+
+    content = playlist_path.read_text()
+    assert "#EXTM3U" in content
+    assert "01_Disc1_Song_1.flac" in content
+    assert "02_Disc1_Song_2.flac" in content
+    # Kein CD-Prefix bei Single-Disc
+    assert "CD1/" not in content
+
+
+def test_generate_playlist_multi_disc(tmp_path: Path):
+    """M3U für Multi-CD: CD-Prefix in Pfaden."""
+    album = _make_album(n_tracks=2, n_discs=2)
+
+    cd1 = tmp_path / "CD1"
+    cd2 = tmp_path / "CD2"
+    cd1.mkdir()
+    cd2.mkdir()
+    (cd1 / "01_Disc1_Song_1.flac").touch()
+    (cd1 / "02_Disc1_Song_2.flac").touch()
+    (cd2 / "01_Disc2_Song_1.flac").touch()
+    (cd2 / "02_Disc2_Song_2.flac").touch()
+
+    playlist_path = generate_playlist(album, tmp_path)
+    content = playlist_path.read_text()
+
+    assert "CD1/01_Disc1_Song_1.flac" in content
+    assert "CD2/01_Disc2_Song_1.flac" in content
+
+
+def test_generate_playlist_filename(tmp_path: Path):
+    """Playlist-Dateiname ist sanitierter Albumname."""
+    album = Album(
+        artist="A",
+        album="Mein Album",
+        discs=[Disc(disc_number=1, tracks=[Track(track_number=1, title="Song")])],
+    )
+    playlist_path = generate_playlist(album, tmp_path)
+    assert playlist_path.name == "Mein_Album.m3u"
+
+
+def test_generate_playlist_extinf_contains_title(tmp_path: Path):
+    """#EXTINF-Einträge enthalten den originalen Titel."""
+    album = Album(
+        artist="A",
+        album="X",
+        discs=[
+            Disc(
+                disc_number=1,
+                tracks=[Track(track_number=1, title="Für Elise")],
+            )
+        ],
+    )
+    (tmp_path / "01_Für_Elise.flac").touch()
+    playlist_path = generate_playlist(album, tmp_path)
+    content = playlist_path.read_text()
+    assert "#EXTINF:0,Für Elise" in content
+
+
+def test_generate_playlist_fallback_if_file_missing(tmp_path: Path):
+    """Wenn Audiodatei fehlt, wird Fallback-Name erzeugt (kein Absturz)."""
+    album = Album(
+        artist="A",
+        album="X",
+        discs=[Disc(disc_number=1, tracks=[Track(track_number=1, title="Ghost")])],
+    )
+    # Keine Audiodatei anlegen
+    playlist_path = generate_playlist(album, tmp_path)
+    content = playlist_path.read_text()
+    assert "01_Ghost.flac" in content