v0.45.0: copying songs pastes into other apps as a song list

Ctrl+C (and Cut) on selected songs now also puts plain text on the
clipboard — one "Artist - Title" per line, in the order the table shows —
so a whole playlist pastes into a message or a document. Pasting back into
a playlist still reads the songs themselves, as before.

tests/test_round79.py

@@ -227,3 +227,58 @@ class TestLaserDiagram:
         assert pitched[2].x() != pytest.approx(square[2].x())
         # A square screen's vertical edges are vertical.
         assert square[1].x() == pytest.approx(square[2].x())
+
+
+# --------------------------------------------------------------------------
+# 5. Copying songs gives other apps a song list
+# --------------------------------------------------------------------------
+
+def _table(tracks, playlist_mode=True):
+    from lintunes.gui.track_table import TrackTableView
+    table = TrackTableView(playlist_mode=playlist_mode)
+    table.set_source_playlist("PID")
+    table.set_tracks(tracks)
+    return table
+
+
+def _songs():
+    from lintunes.models import Track
+    return [Track(track_id=1, name="Low Tide", artist="The Wheelhouse"),
+            Track(track_id=2, name="Café Noir", artist="Marguerite Vaux"),
+            Track(track_id=3, name="Orphan Take", artist="")]
+
+
+class TestCopyAsText:
+    def test_select_all_copy_pastes_as_a_list(self, qapp):
+        from lintunes.gui.track_table import parse_tracks_mime
+        table = _table(_songs())
+        table.selectAll()
+        table.copy_selection()
+        mime = QApplication.clipboard().mimeData()
+        assert mime.text() == ("The Wheelhouse - Low Tide\n"
+                               "Marguerite Vaux - Café Noir\n"
+                               "Orphan Take")
+        # …and pasting into a playlist still reads the songs themselves.
+        assert parse_tracks_mime(mime)["track_ids"] == [1, 2, 3]
+
+    def test_the_list_follows_the_order_shown(self, qapp):
+        from PyQt6.QtCore import Qt
+        table = _table(_songs(), playlist_mode=False)
+        name = table.model_.fields.index("name")
+        table.sortByColumn(name, Qt.SortOrder.AscendingOrder)
+        table.selectAll()
+        table.copy_selection()
+        assert QApplication.clipboard().text().splitlines() == [
+            "Marguerite Vaux - Café Noir", "The Wheelhouse - Low Tide",
+            "Orphan Take"]
+
+    def test_cut_carries_the_list_too(self, qapp):
+        table = _table(_songs())
+        table.selectRow(0)
+        table.cut_selection()
+        assert QApplication.clipboard().text() == "The Wheelhouse - Low Tide"
+
+    def test_untitled_song(self, qapp):
+        from lintunes.gui.track_table import song_line
+        from lintunes.models import Track
+        assert song_line(Track(track_id=9, name="", artist="X")) == "X - Untitled"