Marshmallow ValidationError 'field_name' issue

Question

I have one question concerning newer versions of Marhsmallow API. In our project we are currently using Marshmallow version 3.0.0b14; and we have the following tests functions defined (work perfectly):

from marshmallow.exceptions import ValidationError
from hamcrest import assert_that, calling, has_properties, has_item, not_

def test_invalid_expiration(self):
        invalid_values = [None, True, False, 'foobar', 0]

        for value in invalid_values:
            body = {'expiration': value}
            assert_that(
                calling(self.schema.load).with_args(body),
                raises(ValidationError).matching(
                    has_properties(field_names=has_item('expiration'))
                ),
            )

def test_that_acces_type_offline_requires_a_client_id(self):
        body = {'access_type': 'offline'}

        assert_that(
            calling(self.schema.load).with_args(body),
            raises(ValidationError).matching(
                has_properties(field_names=has_item('_schema'))
            ),
        )

def test_that_the_access_type_is_online_when_using_a_refresh_token(self):
        body = {'refresh_token': 'foobar', 'client_id': 'x'}

        assert_that(calling(self.schema.load).with_args(body), not_(raises(Exception)))

        assert_that(
            calling(self.schema.load).with_args({'access_type': 'online', **body}),
            not_(raises(Exception)),
        )

        assert_that(
            calling(self.schema.load).with_args({'access_type': 'offline', **body}),
            raises(ValidationError).matching(
                has_properties(field_names=has_item('_schema'))
            ),
        )

def test_that_a_refresh_token_requires_a_client_id(self):
        body = {'refresh_token': 'the-token'}

        assert_that(
            calling(self.schema.load).with_args({'client_id': 'x', **body}),
            not_(raises(Exception)),
        )

        assert_that(
            calling(self.schema.load).with_args(body),
            raises(ValidationError).matching(
                has_properties(field_names=has_item('_schema'))
            ),
        )

Now, we are trying to bump the version of Marshmallow in order to upgrade it to 3.10.0; however, in this version, field_names from ValidationError has been removed and replaced by field_name (which is always equal to _schema if i am correct).

So my question is the following: how can we change/modify the tests posted above so that we don't have any error when executing them. This is what I have tried so far:

raises(ValidationError).matching(
                     has_properties(messages=has_item('expiration'))
                 ),


raises(ValidationError).matching(
                 has_properties(messages=has_item('_schema'))
             ),

We did not match on the new field_name since it is always equal to _schema; so we went on matching/probing the messages field; the following issue relates to a similar issue to what we are facing:

https://github.com/marshmallow-code/marshmallow/issues/1499