sidebar: Move the Filter into a Gtk.CenterBox

I'm going to add a button to jump to the current playlist, and the first
step is to add an area to put it in the sidebar.

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

emmental/sidebar/__init__.py

@@ -23,7 +23,8 @@ class Card(Gtk.Box):
         """Set up the Sidebar widget."""
         super().__init__(sql=sql, orientation=Gtk.Orientation.VERTICAL,
                          sensitive=False, **kwargs)
-        self._filter = entry.Filter("playlists")
+        self._header = Gtk.CenterBox()
+        self._filter = entry.Filter("playlists", hexpand=True)
         self._playlists = playlist.Section(self.sql.playlists)
         self._artists = artist.Section(self.sql.artists, self.sql.albums)
         self._genres = genre.Section(self.sql.genres)
@@ -31,7 +32,8 @@ class Card(Gtk.Box):
         self._libraries = library.Section(self.sql.libraries)
         self._view = section.View(sql)
 
-        self.append(self._filter)
+        self._header.set_center_widget(self._filter)
+        self.append(self._header)
 
         for sect in [self._playlists, self._artists, self._genres,
                      self._decades, self._libraries]:
@@ -46,6 +48,7 @@ class Card(Gtk.Box):
         self._filter.connect("search-changed", self.__search_changed)
         self.sql.connect("table-loaded", self.__table_loaded)
 
+        self._header.add_css_class("toolbar")
         self.add_css_class("card")
 
     def __search_changed(self, entry: entry.Filter) -> None:

tests/sidebar/test_sidebar.py

@@ -25,13 +25,21 @@ class TestSidebar(tests.util.TestCase):
 
         self.assertTrue(self.sidebar.has_css_class("card"))
 
+    def test_header(self):
+        """Test the Sidebar header."""
+        self.assertIsInstance(self.sidebar._header, Gtk.CenterBox)
+        self.assertEqual(self.sidebar.get_first_child(), self.sidebar._header)
+        self.assertTrue(self.sidebar._header.has_css_class("toolbar"))
+
     def test_filter(self):
         """Test the Sidebar filter entry."""
         self.assertIsInstance(self.sidebar._filter, emmental.entry.Filter)
 
-        self.assertEqual(self.sidebar.get_first_child(), self.sidebar._filter)
+        self.assertEqual(self.sidebar._header.get_center_widget(),
+                         self.sidebar._filter)
         self.assertEqual(self.sidebar._filter.get_placeholder_text(),
                          "type to filter playlists")
+        self.assertTrue(self.sidebar._filter.get_hexpand())
 
         with unittest.mock.patch.object(self.sql, "filter") as mock_filter:
             self.sidebar._filter.set_text("test text")
@@ -78,7 +86,7 @@ class TestSidebar(tests.util.TestCase):
         """Test that sidebar sections are in the View."""
         self.assertIsInstance(self.sidebar._view,
                               emmental.sidebar.section.View)
-        self.assertEqual(self.sidebar._filter.get_next_sibling(),
+        self.assertEqual(self.sidebar._header.get_next_sibling(),
                          self.sidebar._view)
 
         self.assertListEqual(self.sidebar._view._sections,