sidebar: Create a PlaylistTitle widget

This widget sets the Title::subtitle property to a nicely formatted
string based on the number set to the 'count' property.

Signed-off-by: Anna Schumaker <Anna@NoWheyCreamery.com>

emmental/sidebar/title.py

@@ -31,3 +31,18 @@ class Title(Gtk.Box):
 
         self.append(self._title)
         self.append(self._subtitle)
+
+
+class PlaylistTitle(Title):
+    """A title widget for displaying playlist size."""
+
+    count = GObject.Property(type=int)
+
+    def __init__(self, title: str = "", **kwargs):
+        """Initialize a Playlist Title widget."""
+        super().__init__(title=title, subtitle="-- tracks", **kwargs)
+        self.connect("notify::count", self.__update_subtitle)
+
+    def __update_subtitle(self, title: Title, param) -> None:
+        s_count = "s" if self.count != 1 else ""
+        self.subtitle = f"{self.count} track{s_count}"

tests/sidebar/test_title.py

@@ -62,3 +62,28 @@ class TestTitle(unittest.TestCase):
 
         title2 = emmental.sidebar.title.Title(subtitle="Other Subtitle")
         self.assertEqual(title2._subtitle.get_text(), "Other Subtitle")
+
+
+class TestPlaylistTitle(unittest.TestCase):
+    """Test our title widget configured for displaying playlist size."""
+
+    def setUp(self):
+        """Set up common variables."""
+        self.title = emmental.sidebar.title.PlaylistTitle()
+
+    def test_init(self):
+        """Test that the PlaylistTitle is configured correctly."""
+        self.assertIsInstance(self.title, emmental.sidebar.title.Title)
+        self.assertEqual(self.title.subtitle, "-- tracks")
+        self.assertEqual(self.title.count, 0)
+
+    def test_count(self):
+        """Test changing the count property."""
+        self.title.count = 0
+        self.assertEqual(self.title.subtitle, "0 tracks")
+
+        self.title.count = 1
+        self.assertEqual(self.title.subtitle, "1 track")
+
+        self.title.count = 2
+        self.assertEqual(self.title.subtitle, "2 tracks")