Repository: zopefoundation/zope.schema (language: python)

Issue:
DeprecationWarnings with Python 3.11a1
### What I did:

`tox -e py311`

### What I expect to happen:

Successful run without deprecation warnings.

### What actually happened:

Successful run (yeah!) but a load of deprecation warnings like this:

```
.../lib/python3.11/unittest/case.py:646: DeprecationWarning: It is deprecated to return a value!=None from a test case (<bound method InterfaceConformanceTestsMixin.test_class_conforms_to_iface of <zope.schema.tests.test__bootstrapfields.BoolTests testMethod=test_class_conforms_to_iface>>)
  return self.run(*args, **kwds)
```

The reason seems to be: 
https://github.com/zopefoundation/zope.schema/blob/9378f5ad3dc73971a7be513a8ac63c5f0e3dbce4/src/zope/schema/tests/test__bootstrapfields.py#L43-L57

Those methods are used in some child classes for super calls but in others they are not overwritten.

### What version of Python and Zope/Addons I am using:

Python 3.11a1 on `master` of `zope.schema`.


Discussion / hints:

Fix patch:
diff --git a/CHANGES.rst b/CHANGES.rst
index 2806385..b75365d 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -11,6 +11,9 @@
 
 - Drop ``zope.schema._compat`` module.
 
+- Fix test deprecation warning on Python 3.11.
+  (`#112 <https://github.com/zopefoundation/zope.schema/issues/112>`_)
+
 6.2.1 (2022-09-14)
 ==================
 


Test patch:
diff --git a/src/zope/schema/tests/test__bootstrapfields.py b/src/zope/schema/tests/test__bootstrapfields.py
index 862d590..1cb7630 100644
--- a/src/zope/schema/tests/test__bootstrapfields.py
+++ b/src/zope/schema/tests/test__bootstrapfields.py
@@ -47,7 +47,6 @@ def test_class_conforms_to_iface(self):
         __traceback_info__ = cls
         for iface in self._getTargetInterfaces():
             verifyClass(iface, cls)
-        return verifyClass
 
     def test_instance_conforms_to_iface(self):
         from zope.interface.verify import verifyObject
@@ -55,7 +54,6 @@ def test_instance_conforms_to_iface(self):
         __traceback_info__ = instance
         for iface in self._getTargetInterfaces():
             verifyObject(iface, instance)
-        return verifyObject
 
     def test_iface_is_first_in_sro(self):
         from zope.interface import implementedBy
@@ -1229,17 +1227,20 @@ def _getTargetInterface(self):
         return INumber
 
     def test_class_conforms_to_iface(self):
+        from zope.interface.verify import verifyClass
+
         from zope.schema._bootstrapinterfaces import IFromBytes
         from zope.schema._bootstrapinterfaces import IFromUnicode
-        verifyClass = super(NumberTests, self).test_class_conforms_to_iface()
+        super(NumberTests, self).test_class_conforms_to_iface()
         verifyClass(IFromUnicode, self._getTargetClass())
         verifyClass(IFromBytes, self._getTargetClass())
 
     def test_instance_conforms_to_iface(self):
+        from zope.interface.verify import verifyObject
+
         from zope.schema._bootstrapinterfaces import IFromBytes
         from zope.schema._bootstrapinterfaces import IFromUnicode
-        verifyObject = (
-            super(NumberTests, self).test_instance_conforms_to_iface())
+        super(NumberTests, self).test_instance_conforms_to_iface()
         verifyObject(IFromUnicode, self._makeOne())
         verifyObject(IFromBytes, self._makeOne())