add tests for widget garbage collection

# Conflicts:
#	testbed/tests/widgets/test_webview.py

testbed/tests/widgets/test_activityindicator.py

@@ -1,3 +1,6 @@
+import gc
+import weakref
+
 import pytest
 
 import toga
@@ -15,6 +18,18 @@ async def widget():
     return toga.ActivityIndicator()
 
 
+async def test_cleanup():
+    skip_on_platforms("android", "iOS", "windows")
+
+    widget = toga.ActivityIndicator()
+    ref = weakref.ref(widget)
+
+    del widget
+    gc.collect()
+
+    assert ref() is None
+
+
 async def test_start_stop(widget, probe):
     "The activity indicator can be started and stopped"
     # Widget should be initially stopped

testbed/tests/widgets/test_box.py

@@ -1,3 +1,6 @@
+import gc
+import weakref
+
 import pytest
 
 import toga
@@ -15,3 +18,13 @@
 @pytest.fixture
 async def widget():
     return toga.Box(style=Pack(width=100, height=200))
+
+
+async def test_cleanup():
+    widget = toga.Box(style=Pack(width=100, height=200))
+    ref = weakref.ref(widget)
+
+    del widget
+    gc.collect()
+
+    assert ref() is None

testbed/tests/widgets/test_button.py

@@ -1,3 +1,5 @@
+import gc
+import weakref
 from unittest.mock import Mock
 
 from pytest import approx, fixture
@@ -31,6 +33,16 @@ async def widget():
     return toga.Button("Hello")
 
 
+async def test_cleanup():
+    widget = toga.Button("Hello")
+    ref = weakref.ref(widget)
+
+    del widget
+    gc.collect()
+
+    assert ref() is None
+
+
 async def test_text(widget, probe):
     "The text displayed on a button can be changed"
     initial_height = probe.height

testbed/tests/widgets/test_dateinput.py

@@ -1,3 +1,5 @@
+import gc
+import weakref
 from datetime import date, datetime, timedelta
 from unittest.mock import Mock, call
 
@@ -82,6 +84,18 @@ async def widget():
     return toga.DateInput()
 
 
+async def test_cleanup():
+    skip_on_platforms("macOS", "iOS", "linux")
+
+    widget = toga.DateInput()
+    ref = weakref.ref(widget)
+
+    del widget
+    gc.collect()
+
+    assert ref() is None
+
+
 async def test_init():
     "Properties can be set in the constructor"
     skip_on_platforms("macOS", "iOS", "linux")

testbed/tests/widgets/test_divider.py

@@ -1,3 +1,6 @@
+import gc
+import weakref
+
 import pytest
 
 import toga
@@ -17,6 +20,18 @@ async def widget():
     return toga.Divider()
 
 
+async def test_cleanup():
+    skip_on_platforms("android", "iOS")
+
+    widget = toga.Divider()
+    ref = weakref.ref(widget)
+
+    del widget
+    gc.collect()
+
+    assert ref() is None
+
+
 async def test_directions(widget, probe):
     "The divider has the right size as direction is changed"
     # Widget should be initially horizontal.

testbed/tests/widgets/test_imageview.py

@@ -1,3 +1,6 @@
+import gc
+import weakref
+
 import pytest
 
 import toga
@@ -17,6 +20,16 @@ async def widget():
     return toga.ImageView(image="resources/sample.png")
 
 
+async def test_cleanup():
+    widget = toga.ImageView(image="resources/sample.png")
+    ref = weakref.ref(widget)
+
+    del widget
+    gc.collect()
+
+    assert ref() is None
+
+
 async def test_implicit_size(widget, probe, container_probe):
     """If the image view size is implicit, the image provides flexible size hints."""
 

testbed/tests/widgets/test_label.py

@@ -1,3 +1,6 @@
+import gc
+import weakref
+
 from pytest import approx, fixture
 
 import toga
@@ -24,6 +27,16 @@ async def widget():
     return toga.Label("hello, this is a label")
 
 
+async def test_cleanup():
+    widget = toga.Label("hello, this is a label")
+    ref = weakref.ref(widget)
+
+    del widget
+    gc.collect()
+
+    assert ref() is None
+
+
 async def test_multiline(widget, probe):
     """If the label contains multiline text, it resizes vertically."""
 

testbed/tests/widgets/test_multilinetextinput.py

@@ -1,3 +1,6 @@
+import gc
+import weakref
+
 import pytest
 
 import toga
@@ -36,6 +39,16 @@ async def widget():
     return toga.MultilineTextInput(value="Hello", style=Pack(flex=1))
 
 
+async def test_cleanup():
+    widget = toga.MultilineTextInput(value="Hello")
+    ref = weakref.ref(widget)
+
+    del widget
+    gc.collect()
+
+    assert ref() is None
+
+
 @pytest.fixture
 def verify_font_sizes():
     # We can't verify font sizes inside the MultilineTextInput

testbed/tests/widgets/test_numberinput.py

@@ -1,3 +1,5 @@
+import gc
+import weakref
 from decimal import Decimal
 from unittest.mock import Mock, call
 
@@ -30,6 +32,16 @@ async def widget():
     return toga.NumberInput(value="1.23", step="0.01")
 
 
+async def test_cleanup():
+    widget = toga.NumberInput(value="1.23", step="0.01")
+    ref = weakref.ref(widget)
+
+    del widget
+    gc.collect()
+
+    assert ref() is None
+
+
 @pytest.fixture
 def verify_font_sizes():
     # We can't verify font width inside the TextInput

testbed/tests/widgets/test_optioncontainer.py

@@ -1,3 +1,5 @@
+import gc
+import weakref
 from unittest.mock import Mock
 
 import pytest
@@ -71,6 +73,18 @@ async def widget(content1, content2, content3, on_select_handler):
     )
 
 
+async def test_cleanup():
+    skip_on_platforms("android", "iOS")
+
+    widget = toga.OptionContainer(content=[("Tab 1", toga.Box())])
+    ref = weakref.ref(widget)
+
+    del widget
+    gc.collect()
+
+    assert ref() is None
+
+
 async def test_select_tab(
     widget,
     probe,

testbed/tests/widgets/test_passwordinput.py

@@ -1,3 +1,6 @@
+import gc
+import weakref
+
 import pytest
 
 import toga
@@ -38,6 +41,16 @@ async def widget():
     return toga.PasswordInput(value="sekrit")
 
 
+async def test_cleanup():
+    widget = toga.PasswordInput(value="sekrit")
+    ref = weakref.ref(widget)
+
+    del widget
+    gc.collect()
+
+    assert ref() is None
+
+
 @pytest.fixture
 def verify_font_sizes():
     # We can't verify font width inside the TextInput

testbed/tests/widgets/test_progressbar.py

@@ -1,3 +1,7 @@
+import asyncio
+import gc
+import weakref
+
 import pytest
 
 import toga
@@ -19,6 +23,16 @@ async def widget():
     return toga.ProgressBar(max=100, value=5)
 
 
+async def test_cleanup():
+    widget = toga.ProgressBar(max=100, value=5)
+    ref = weakref.ref(widget)
+
+    del widget
+    gc.collect()
+
+    assert ref() is None
+
+
 async def test_start_stop_determinate(widget, probe):
     "A determinate progress bar can be started and stopped"
     # Widget should be initially stopped and determinate

testbed/tests/widgets/test_scrollcontainer.py

@@ -1,3 +1,5 @@
+import gc
+import weakref
 from unittest.mock import Mock
 
 import pytest
@@ -72,6 +74,16 @@ async def widget(content, on_scroll):
     )
 
 
+async def test_cleanup():
+    widget = toga.ScrollContainer(content=toga.Box())
+    ref = weakref.ref(widget)
+
+    del widget
+    gc.collect()
+
+    assert ref() is None
+
+
 async def test_clear_content(widget, probe, small_content):
     "Widget content can be cleared and reset"
     assert probe.document_width == probe.width - probe.scrollbar_inset

testbed/tests/widgets/test_selection.py

@@ -1,3 +1,5 @@
+import gc
+import weakref
 from unittest.mock import Mock
 
 import pytest
@@ -40,6 +42,16 @@ async def widget():
     return toga.Selection(items=["first", "second", "third"])
 
 
+async def test_cleanup():
+    widget = toga.Selection(items=["first", "second", "third"])
+    ref = weakref.ref(widget)
+
+    del widget
+    gc.collect()
+
+    assert ref() is None
+
+
 @pytest.fixture
 def verify_font_sizes():
     # Font size does not affect the width of this widget.

testbed/tests/widgets/test_slider.py

@@ -1,3 +1,5 @@
+import gc
+import weakref
 from math import pi
 from unittest.mock import Mock
 
@@ -34,6 +36,16 @@ async def widget():
     return toga.Slider()
 
 
+async def test_cleanup():
+    widget = toga.Slider()
+    ref = weakref.ref(widget)
+
+    del widget
+    gc.collect()
+
+    assert ref() is None
+
+
 @fixture
 def on_change(widget):
     handler = Mock()

testbed/tests/widgets/test_splitcontainer.py

@@ -1,3 +1,6 @@
+import gc
+import weakref
+
 import pytest
 from pytest import approx
 
@@ -6,7 +9,7 @@
 from toga.constants import Direction
 from toga.style.pack import Pack
 
-from ..conftest import xfail_on_platforms
+from ..conftest import skip_on_platforms
 from .probe import get_probe
 from .properties import (  # noqa: F401
     test_enable_noop,
@@ -56,10 +59,22 @@ async def content3_probe(content3):
 
 @pytest.fixture
 async def widget(content1, content2):
-    xfail_on_platforms("android", "iOS")
+    skip_on_platforms("android", "iOS")
     return toga.SplitContainer(content=[content1, content2], style=Pack(flex=1))
 
 
+async def test_cleanup():
+    skip_on_platforms("android", "iOS")
+
+    widget = toga.SplitContainer(content=[toga.Box(), toga.Box()])
+    ref = weakref.ref(widget)
+
+    del widget
+    gc.collect()
+
+    assert ref() is None
+
+
 async def test_set_content(
     widget,
     probe,