tests/test_sync_to_ipod.py

@@ -271,3 +271,67 @@ def test_the_scan_reads_from_the_mirror_not_the_device():
 
     assert 'ln -s "$mirror"' in script
     assert 'cd "$scratch"' in script
+
+
+def can_bind_mount():
+    """User namespaces let an unprivileged process bind mount. Not everywhere,
+    notably not inside some containers, so the test that needs it skips."""
+    return (
+        subprocess.run(
+            ["unshare", "-Umr", "true"], capture_output=True, check=False
+        ).returncode
+        == 0
+    )
+
+
+@pytest.mark.skipif(not can_bind_mount(), reason="needs unprivileged user namespaces")
+def test_the_database_lands_at_the_device_root_not_the_music_folder(tmp_path):
+    """The two tools disagree about where the root is. rsync copies artist
+    folders into <device>/Music; the database tool must run one level up, where
+    .rockbox lives, and must record /Music/... paths while reading the bytes
+    from the mirror. device_prefix is what reconciles them.
+    """
+    mirror = tmp_path / "mirror" / "Pendulum" / "Immersion"
+    mirror.mkdir(parents=True)
+    (mirror / "01.mp3").write_bytes(b"not really an mp3")
+    card = tmp_path / "card"
+    (card / ".rockbox").mkdir(parents=True)
+    (card / "Music").mkdir()
+    device = tmp_path / "device"
+    device.mkdir()
+
+    tool = tmp_path / "fake-database"
+    # Records where it was run and what it could see, which is the whole
+    # question; producing a real database needs Rockbox's builder.
+    tool.write_text(
+        "#!/bin/sh\n"
+        "printf '%s\\n' \"$PWD\" > .rockbox/where.txt\n"
+        "ls Music/ > .rockbox/saw.txt\n"
+        "echo db > .rockbox/database_0.tcd\n"
+    )
+    tool.chmod(0o755)
+
+    script = (
+        f"mount --bind {card} {device} && "
+        f"XDG_CACHE_HOME={tmp_path / 'cache'} MUSIC_MIRROR_DATABASE_TOOL={tool} "
+        f"bash {SCRIPT} -f -S -U -Q {tmp_path / 'mirror'} {device / 'Music'}"
+    )
+    result = subprocess.run(
+        ["unshare", "-Umr", "sh", "-c", script], capture_output=True, text=True
+    )
+
+    assert result.returncode == 0, result.stderr
+    # The database lands beside the device root, not inside Music.
+    assert (card / ".rockbox" / "database_0.tcd").is_file()
+    # Only *.tcd is copied across, so the markers stay in the scratch root --
+    # which is itself the point: nothing else is written to the device.
+    scratch = tmp_path / "cache" / "music-mirror" / "database" / ".rockbox"
+    assert not (card / ".rockbox" / "where.txt").exists()
+
+    # It ran in the scratch root, not on the card.
+    where = (scratch / "where.txt").read_text().strip()
+    assert where.endswith("music-mirror/database"), where
+    # ...and could walk into the mirror through a symlink named for the device
+    # prefix, which is how the paths come out as /Music/... while the bytes are
+    # read from somewhere else entirely.
+    assert "Pendulum" in (scratch / "saw.txt").read_text()