Test Suite fails with env variable ETS_DEBUG set to True

When running the following:
```
python etstool.py install --toolkit=pyqt5 --editable
edm shell -e pyface-test-3.6-pyqt5
export ETS_DEBUG=True
python -m unittest
```

I see the following failures (I had to truncate the excessively long traceback):

```
$ python -m unittest
2021-07-07 10:43:34.259 Python[56601:16840268] ApplePersistenceIgnoreState: Existing state will not be touched. New state will be written to /var/folders/j9/ps8s26f91_1_lgf7mtd4smyr0000gn/T/org.python.python.savedState
......................................................................................Did not find name 'fallback' on
......../Users/aayres/Desktop/pyface/pyface/base_toolkit.py:190: DeprecationWarning: SelectableGroups dict interface is deprecated. Use select.
entry_point_group = importlib_metadata.entry_points()[entry_point]
EEE...E.....................................................................................................................EE..............................................................................................................s.........................................EEEEEEEEEEEE......EEEEs...---- ApplicationExit raised ----
Traceback (most recent call last):
File "/Users/aayres/Desktop/pyface/pyface/application.py", line 174, in run
run = self._run()
File "/Users/aayres/Desktop/pyface/pyface/tests/test_application.py", line 72, in _run
raise ApplicationExit("error message")
pyface.application.ApplicationExit: error message
..Error preparing for application exit
Traceback (most recent call last):
File "/Users/aayres/Desktop/pyface/pyface/application.py", line 215, in exit
self._prepare_exit()
File "/Users/aayres/Desktop/pyface/pyface/tests/test_application.py", line 84, in _prepare_exit
raise Exception("Exit preparation failed")
Exception: Exit preparation failed
.....EEEEEEEEEEEEEEEEEE/Users/aayres/Desktop/pyface/pyface/base_toolkit.py:259: DeprecationWarning: SelectableGroups dict interface is deprecated. Use select.
plugin for plugin in importlib_metadata.entry_points()[entry_point]
......s............................................EEEEEEEEEEEEEEEEEEE...............EEEEEEEEEEEEEE......EEEEEEE..EEEEEEEEEEEEEE..../Users/aayres/Desktop/pyface/pyface/tests/test_toolkit.py:36: DeprecationWarning: SelectableGroups dict interface is deprecated. Use select.
plugins = {ep.name for ep in entry_points()['pyface.toolkits']}
...E.EEEEEEEEEEEEE........EEEEEEEEEEEEEEEEEEEEEEEE...E..EEEE/Users/aayres/Desktop/pyface/pyface/ui/qt4/mimedata.py:57: RuntimeWarning: Could not pickle dragged object . at 0x7fe7dc21ed08>, using application/x-ets-qt4-instance-no-pickle mimetype instead
RuntimeWarning,
........./Users/aayres/Desktop/pyface/pyface/ui/qt4/mimedata.py:57: RuntimeWarning: Could not pickle dragged object . at 0x7fe7dc21ed08>, using application/x-ets-qt4-instance-no-pickle mimetype instead
RuntimeWarning,
..........EEEEEEEE.../Users/aayres/Desktop/pyface/pyface/base_toolkit.py:190: DeprecationWarning: SelectableGroups dict interface is deprecated. Use select.
entry_point_group = importlib_metadata.entry_points()[entry_point]
EEEEEEEEEEEsssssssssssssssE............................................................................EE
======================================================================
ERROR: test_traitsui_widget_action (pyface.action.tests.test_traitsui_widget_action.TestTraitsUIWidgetAction)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/Users/aayres/Desktop/pyface/pyface/action/tests/test_traitsui_widget_action.py", line 50, in test_traitsui_widget_action
from traitsui.api import View, Item
File "/Users/aayres/.edm/envs/pyface-test-3.6-pyqt5/lib/python3.6/site-packages/traitsui/api.py", line 256, in
from .editors.api import ArrayEditor
File "/Users/aayres/.edm/envs/pyface-test-3.6-pyqt5/lib/python3.6/site-packages/traitsui/editors/__init__.py", line 16, in
from .api import ArrayEditor
File "/Users/aayres/.edm/envs/pyface-test-3.6-pyqt5/lib/python3.6/site-packages/traitsui/editors/api.py", line 86, in
from .code_editor import CodeEditor
File "/Users/aayres/.edm/envs/pyface-test-3.6-pyqt5/lib/python3.6/site-packages/traitsui/editors/code_editor.py", line 21, in
class CodeEditor(EditorFactory):
File "/Users/aayres/.edm/envs/pyface-test-3.6-pyqt5/lib/python3.6/site-packages/traitsui/editors/code_editor.py", line 33, in CodeEditor
mark_color = Color(0xECE9D8)
File "/Users/aayres/.edm/envs/pyface-test-3.6-pyqt5/lib/python3.6/site-packages/traits/trait_factory.py", line 40, in __call__
return self.maker_function(*args, **metadata)
File "/Users/aayres/.edm/envs/pyface-test-3.6-pyqt5/lib/python3.6/site-packages/traitsui/toolkit_traits.py", line 43, in ColorTrait
return toolkit().color_trait(*args, **traits)
File "/Users/aayres/.edm/envs/pyface-test-3.6-pyqt5/lib/python3.6/site-packages/traitsui/toolkit.py", line 110, in toolkit
_toolkit = find_toolkit("traitsui.toolkits")
File "/Users/aayres/Desktop/pyface/pyface/base_toolkit.py", line 256, in find_toolkit
return import_toolkit(ETSConfig.toolkit, entry_point)
File "/Users/aayres/Desktop/pyface/pyface/base_toolkit.py", line 220, in import_toolkit
raise RuntimeError(msg)
RuntimeError: No traitsui.toolkits plugin could be loaded for qt4

...

======================================================================
ERROR: pyface.ui.qt4.util.tests.test_modal_dialog_tester (unittest.loader._FailedTest)
----------------------------------------------------------------------
ImportError: Failed to import test module: pyface.ui.qt4.util.tests.test_modal_dialog_tester
Traceback (most recent call last):
File "/Users/aayres/.edm/envs/pyface-test-3.6-pyqt5/lib/python3.6/unittest/loader.py", line 428, in _find_test_path
module = self._get_module_from_name(name)
File "/Users/aayres/.edm/envs/pyface-test-3.6-pyqt5/lib/python3.6/unittest/loader.py", line 369, in _get_module_from_name
__import__(name)
File "/Users/aayres/Desktop/pyface/pyface/ui/qt4/util/tests/test_modal_dialog_tester.py", line 18, in
from pyface.api import Dialog, MessageDialog, OK, CANCEL
File "/Users/aayres/Desktop/pyface/pyface/api.py", line 148, in
from .expandable_panel import ExpandablePanel
File "/Users/aayres/Desktop/pyface/pyface/expandable_panel.py", line 18, in
ExpandablePanel = toolkit_object("expandable_panel:ExpandablePanel")
File "/Users/aayres/Desktop/pyface/pyface/base_toolkit.py", line 126, in __call__
module = import_module(mname, package)
File "/Users/aayres/.edm/envs/pyface-test-3.6-pyqt5/lib/python3.6/importlib/__init__.py", line 126, in import_module
return _bootstrap._gcd_import(name[level:], package, level)
ModuleNotFoundError: No module named 'pyface.ui.qt4.expandable_panel'

======================================================================
ERROR: pyface.ui.qt4.workbench.tests.test_workbench_window_layout (unittest.loader._FailedTest)
----------------------------------------------------------------------
ImportError: Failed to import test module: pyface.ui.qt4.workbench.tests.test_workbench_window_layout
Traceback (most recent call last):
File "/Users/aayres/.edm/envs/pyface-test-3.6-pyqt5/lib/python3.6/unittest/loader.py", line 428, in _find_test_path
module = self._get_module_from_name(name)
File "/Users/aayres/.edm/envs/pyface-test-3.6-pyqt5/lib/python3.6/unittest/loader.py", line 369, in _get_module_from_name
__import__(name)
File "/Users/aayres/Desktop/pyface/pyface/ui/qt4/workbench/tests/test_workbench_window_layout.py", line 16, in
from pyface.ui.qt4.workbench.workbench_window_layout import (
File "/Users/aayres/Desktop/pyface/pyface/ui/qt4/workbench/workbench_window_layout.py", line 27, in
from pyface.workbench.i_workbench_window_layout import MWorkbenchWindowLayout
File "/Users/aayres/Desktop/pyface/pyface/workbench/i_workbench_window_layout.py", line 19, in
from .i_view import IView
File "/Users/aayres/Desktop/pyface/pyface/workbench/i_view.py", line 17, in
from pyface.api import ImageResource
File "/Users/aayres/Desktop/pyface/pyface/api.py", line 148, in
from .expandable_panel import ExpandablePanel
File "/Users/aayres/Desktop/pyface/pyface/expandable_panel.py", line 18, in
ExpandablePanel = toolkit_object("expandable_panel:ExpandablePanel")
File "/Users/aayres/Desktop/pyface/pyface/base_toolkit.py", line 126, in __call__
module = import_module(mname, package)
File "/Users/aayres/.edm/envs/pyface-test-3.6-pyqt5/lib/python3.6/importlib/__init__.py", line 126, in import_module
return _bootstrap._gcd_import(name[level:], package, level)
ModuleNotFoundError: No module named 'pyface.ui.qt4.expandable_panel'

======================================================================
ERROR: pyface.ui.wx.util.tests.test_image_helpers (unittest.loader._FailedTest)
----------------------------------------------------------------------
ImportError: Failed to import test module: pyface.ui.wx.util.tests.test_image_helpers
Traceback (most recent call last):
File "/Users/aayres/.edm/envs/pyface-test-3.6-pyqt5/lib/python3.6/unittest/loader.py", line 428, in _find_test_path
module = self._get_module_from_name(name)
File "/Users/aayres/.edm/envs/pyface-test-3.6-pyqt5/lib/python3.6/unittest/loader.py", line 369, in _get_module_from_name
__import__(name)
File "/Users/aayres/Desktop/pyface/pyface/ui/wx/util/tests/test_image_helpers.py", line 12, in
import wx
ModuleNotFoundError: No module named 'wx'

======================================================================
ERROR: test_import (pyface.util.tests.test_modal_dialog_tester.TestModalDialogTester)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/Users/aayres/Desktop/pyface/pyface/util/tests/test_modal_dialog_tester.py", line 21, in test_import
from pyface.util.modal_dialog_tester import ModalDialogTester
File "/Users/aayres/Desktop/pyface/pyface/util/modal_dialog_tester.py", line 18, in
"util.modal_dialog_tester:ModalDialogTester"
File "/Users/aayres/Desktop/pyface/pyface/base_toolkit.py", line 126, in __call__
module = import_module(mname, package)
File "/Users/aayres/.edm/envs/pyface-test-3.6-pyqt5/lib/python3.6/importlib/__init__.py", line 126, in import_module
return _bootstrap._gcd_import(name[level:], package, level)
File "/Users/aayres/Desktop/pyface/pyface/ui/qt4/util/modal_dialog_tester.py", line 17, in
from pyface.api import GUI, OK, CANCEL, YES, NO
File "/Users/aayres/Desktop/pyface/pyface/api.py", line 148, in
from .expandable_panel import ExpandablePanel
File "/Users/aayres/Desktop/pyface/pyface/expandable_panel.py", line 18, in
ExpandablePanel = toolkit_object("expandable_panel:ExpandablePanel")
File "/Users/aayres/Desktop/pyface/pyface/base_toolkit.py", line 126, in __call__
module = import_module(mname, package)
File "/Users/aayres/.edm/envs/pyface-test-3.6-pyqt5/lib/python3.6/importlib/__init__.py", line 126, in import_module
return _bootstrap._gcd_import(name[level:], package, level)
ModuleNotFoundError: No module named 'pyface.ui.qt4.expandable_panel'

======================================================================
ERROR: pyface.workbench.tests.test_workbench_window (unittest.loader._FailedTest)
----------------------------------------------------------------------
ImportError: Failed to import test module: pyface.workbench.tests.test_workbench_window
Traceback (most recent call last):
File "/Users/aayres/.edm/envs/pyface-test-3.6-pyqt5/lib/python3.6/unittest/loader.py", line 428, in _find_test_path
module = self._get_module_from_name(name)
File "/Users/aayres/.edm/envs/pyface-test-3.6-pyqt5/lib/python3.6/unittest/loader.py", line 369, in _get_module_from_name
__import__(name)
File "/Users/aayres/Desktop/pyface/pyface/workbench/tests/test_workbench_window.py", line 19, in
from pyface.workbench.api import Workbench
File "/Users/aayres/Desktop/pyface/pyface/workbench/api.py", line 22, in
from .i_view import IView
File "/Users/aayres/Desktop/pyface/pyface/workbench/i_view.py", line 17, in
from pyface.api import ImageResource
File "/Users/aayres/Desktop/pyface/pyface/api.py", line 148, in
from .expandable_panel import ExpandablePanel
File "/Users/aayres/Desktop/pyface/pyface/expandable_panel.py", line 18, in
ExpandablePanel = toolkit_object("expandable_panel:ExpandablePanel")
File "/Users/aayres/Desktop/pyface/pyface/base_toolkit.py", line 126, in __call__
module = import_module(mname, package)
File "/Users/aayres/.edm/envs/pyface-test-3.6-pyqt5/lib/python3.6/importlib/__init__.py", line 126, in import_module
return _bootstrap._gcd_import(name[level:], package, level)
ModuleNotFoundError: No module named 'pyface.ui.qt4.expandable_panel'

----------------------------------------------------------------------
Ran 750 tests in 4.557s

FAILED (errors=159, skipped=18)
```

There are 159 errors out of 750 tests run.