How to use the xblock.exceptions.InvalidScopeError function in XBlock

def test_runtime_prevents_student_writes_to_non_student_fields(self):
        rt = xblock_module.Runtime(MockHandler(), is_admin=True)
        usage_id = parse_xml_string(rt, 'Test')

        # Load the block in student role
        rt = xblock_module.Runtime(MockHandler(), student_id='s23')
        block = rt.get_block(usage_id)
        self.assertEqual('Test', block.content)
        block.content = 'Something else'
        try:
            block.save()
            self.fail('Expected InvalidScopeError')
        except xblock.exceptions.InvalidScopeError:
            pass  # Expected exception

        # Load the block in admin role
        rt = xblock_module.Runtime(MockHandler(), is_admin=True)
        block = rt.get_block(usage_id)
        block.content = 'Something else'
        block.save()  # No exception

def _field_data(self, block, name):
        """Return the field data for the field `name` on the :class:`~xblock.core.XBlock` `block`"""
        scope = block.fields[name].scope

        if scope not in self._scope_mappings:
            raise InvalidScopeError(scope)

        return self._scope_mappings[scope]

def delete(self, block, name):
        raise InvalidScopeError("{block}.{name} is read-only, cannot delete".format(block=block, name=name))

def __init__(self, invalid_scope, valid_scopes=None):
        super(InvalidScopeError, self).__init__()
        if valid_scopes:
            self.message = "Invalid scope: {}. Valid scopes are: {}".format(
                invalid_scope,
                valid_scopes,
            )
        else:
            self.message = "Invalid scope: {}".format(invalid_scope)

def set(self, block, name, value):
        raise InvalidScopeError("{block}.{name} is read-only, cannot set".format(block=block, name=name))