[pygobject] tests: add a test failing under PyPy due to missing toggle refs

[Christoph Reiter <creiter src gnome org>]

commit 4ed51b6b89be073cde37bb3e32986c9127446d30
Author: Christoph Reiter <reiter christoph gmail com>
Date:   Mon Apr 2 11:41:36 2018 +0200

    tests: add a test failing under PyPy due to missing toggle refs
    
    Once the vfunc is called all the refs to the instance wrapper are gone
    and under PyPy we get a new wrapper because for some reason toggle
    refs aren't triggered.

 tests/test_overrides_gtk.py | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)
---
diff --git a/tests/test_overrides_gtk.py b/tests/test_overrides_gtk.py
index 0a1d08fd..7ffb5068 100644
--- a/tests/test_overrides_gtk.py
+++ b/tests/test_overrides_gtk.py
@@ -8,6 +8,7 @@ import contextlib
 import unittest
 import time
 import sys
+import gc
 import warnings
 
 from .helper import ignore_gi_deprecation_warnings, capture_glib_warnings
@@ -68,6 +69,27 @@ def realized(widget):
         Gtk.main_iteration()
 
 
+@unittest.skipUnless(Gtk, 'Gtk not available')
+def test_wrapper_toggle_refs():
+    class MyButton(Gtk.Button):
+        def __init__(self, height):
+            Gtk.Button.__init__(self)
+            self._height = height
+
+        def do_get_preferred_height(self):
+            return (self._height, self._height)
+
+    height = 142
+    w = Gtk.Window()
+    b = MyButton(height)
+    w.add(b)
+    b.show_all()
+    del b
+    gc.collect()
+    gc.collect()
+    assert w.get_preferred_size().minimum_size.height == height
+
+
 @unittest.skipUnless(Gtk, 'Gtk not available')
 @ignore_gi_deprecation_warnings
 class TestGtk(unittest.TestCase):