[Question] How to catch an IntegrityError raised in an Entity hook?

[LaundroMat]

Suppose I have this model:

class Car(db.Entity):
    colour = Required(str)

    def before_insert(self):
        if self.colour != 'black':
            raise IntegrityError("You can choose any colour, as long as it's black.")

My test looks like this:

def test_create_car():
    with pytest.raises(IntegrityError) as exc_info:
        with db_session:
            Car(colour="pink")
   assert exc_info.value == "You can choose any colour, as long as it's black."

I'm having trouble finding out how I can check the error message attached to the captured IntegrityError. exc_info.value is an empty string.