playlist: Create a VisibleTracks label

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

playlist/footer.py

@@ -0,0 +1,12 @@
+# Copyright 2021 (c) Anna Schumaker.
+from gi.repository import Gtk
+
+class VisibleTracks(Gtk.Label):
+    def __init__(self):
+        Gtk.Label.__init__(self)
+        self.set_halign(Gtk.Align.START)
+        self.set_hexpand(True)
+
+    def set_count(self, n):
+        s = 's' if n != 1 else ''
+        self.set_text(f"Showing {n} track{s}")

playlist/test_footer.py

@@ -0,0 +1,20 @@
+# Copyright 2021 (c) Anna Schumaker.
+import unittest
+from gi.repository import Gtk
+from . import footer
+
+class TestVisibleTracks(unittest.TestCase):
+    def test_init(self):
+        visible = footer.VisibleTracks()
+        self.assertIsInstance(visible, Gtk.Label)
+        self.assertEqual(visible.get_halign(), Gtk.Align.START)
+        self.assertTrue(visible.get_hexpand())
+
+    def test_count(self):
+        visible = footer.VisibleTracks()
+        visible.set_count(0)
+        self.assertEqual(visible.get_text(), "Showing 0 tracks")
+        visible.set_count(1)
+        self.assertEqual(visible.get_text(), "Showing 1 track")
+        visible.set_count(2)
+        self.assertEqual(visible.get_text(), "Showing 2 tracks")