feat: Merge sequence — add (file/selection), reorder, remove

tests/test_ui_structure.py

@@ -412,3 +412,50 @@ def test_audition_button_present_and_safe(win):
     assert win._btn_audio_play.isChecked() is False
     assert win._btn_audio_play.text() == "▶ Play"
     assert win._audition_proc is None
+
+
+def test_merge_list_add_remove_reorder(win, tmp_path):
+    from PyQt6.QtCore import Qt
+    a = tmp_path / "a.wav"; b = tmp_path / "b.wav"
+    a.write_bytes(b""); b.write_bytes(b"")
+    win._merge_add_paths([str(a), str(b)])
+    assert win._merge_list.count() == 2
+    assert win._merge_list.item(0).data(Qt.ItemDataRole.UserRole) == str(a)
+    win._merge_list.setCurrentRow(1)
+    win._merge_move(-1)                       # move b up
+    assert win._merge_list.item(0).data(Qt.ItemDataRole.UserRole) == str(b)
+    win._merge_list.setCurrentRow(0)
+    win._merge_remove_selected()
+    assert win._merge_list.count() == 1
+
+
+def test_merge_add_selection_no_file_safe(win):
+    win._file_path = ""
+    win._merge_list.clear()
+    win._on_merge_add_selection()             # must not raise
+    assert win._merge_list.count() == 0
+
+
+def test_merge_move_bounds_safe(win, tmp_path):
+    a = tmp_path / "a.wav"; b = tmp_path / "b.wav"; a.write_bytes(b""); b.write_bytes(b"")
+    win._merge_list.clear()
+    win._merge_add_paths([str(a), str(b)])
+    win._merge_list.setCurrentRow(0)
+    win._merge_move(-1)                    # already top -> no-op
+    assert win._merge_list.currentRow() == 0
+    win._merge_list.setCurrentRow(1)
+    win._merge_move(1)                     # already bottom -> no-op
+    assert win._merge_list.currentRow() == 1
+    win._merge_list.setCurrentRow(-1)
+    win._merge_move(1)                     # no selection -> safe
+    win._merge_remove_selected()          # no selection -> safe
+    assert win._merge_list.count() == 2
+
+
+def test_merge_add_stores_duration_role(win, tmp_path):
+    from PyQt6.QtCore import Qt
+    a = tmp_path / "a.wav"; a.write_bytes(b"")
+    win._merge_list.clear()
+    win._merge_add_paths([str(a)])
+    # empty fixture -> ffprobe fails -> duration is None; M4 must tolerate None
+    assert win._merge_list.item(0).data(Qt.ItemDataRole.UserRole + 1) is None