buttons: Create a PopoverButton

This is a MenuButton that already has a popover attached and a property
for setting the popover child directly.

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

emmental/buttons.py

@@ -0,0 +1,20 @@
+# Copyright 2022 (c) Anna Schumaker.
+"""Helper classes for Buttons."""
+from gi.repository import GObject
+from gi.repository import Gtk
+
+
+class PopoverButton(Gtk.MenuButton):
+    """A MenuButton with a Gtk.Popover attached."""
+
+    popover_child = GObject.Property(type=Gtk.Widget)
+
+    def __init__(self, **kwargs):
+        """Initialize a popover.Button."""
+        super().__init__(popover=Gtk.Popover(), **kwargs)
+        self.bind_property("popover-child", self.get_popover(), "child")
+        self.get_popover().set_child(self.popover_child)
+
+    def popdown(self):
+        """Close the popover."""
+        self.get_popover().popdown()

tests/test_buttons.py

@@ -0,0 +1,34 @@
+# Copyright 2022 (c) Anna Schumaker.
+"""Test our button helper classes."""
+import unittest
+import emmental.buttons
+from gi.repository import Gtk
+
+
+class TestPopoverButton(unittest.TestCase):
+    """Test a Popover Button."""
+
+    def setUp(self):
+        """Set up common variables."""
+        self.button = emmental.buttons.PopoverButton()
+
+    def test_button(self):
+        """Test that the popover button is configured correctly."""
+        self.assertIsInstance(self.button, Gtk.MenuButton)
+        self.assertIsInstance(self.button.get_popover(), Gtk.Popover)
+
+    def test_popover_child(self):
+        """Test setting a child widget to the popover button."""
+        self.assertIsNone(self.button.popover_child)
+        self.button.popover_child = Gtk.Label()
+        self.assertEqual(self.button.get_popover().get_child(),
+                         self.button.popover_child)
+
+        button2 = emmental.buttons.PopoverButton(popover_child=Gtk.Label())
+        self.assertIsInstance(button2.popover_child, Gtk.Label)
+        self.assertEqual(button2.get_popover().get_child(),
+                         button2.popover_child)
+
+    def test_popdown(self):
+        """Test the popdown() function."""
+        self.button.popdown()