¿Cómo se devuelven todos los errores del serializador de DRF de una vez?

Estoy probando la elevación de múltiples errores de validación en (UserRegistrationSerializer). Sin embargo, DRF solo devuelve el primer error que se produce: {‘username’: [ErrorDetail(string=’Choose a different username’, code=’invalid’)]}

Espero: {‘username’: [ErrorDetail(string=’Choose a different username’, code=’invalid’)], ‘password2′: [ErrorDetail(string=’Password confirmation failed’, code=’invalid’)]}

¿Cómo se pueden tener en cuenta múltiples errores una vez que se ha validado un serializador como en el ejemplo de la documentación? https://www.django-rest-framework.org/api-guide/serializers/#validation

class TestRegisterationSerializer__002(TestCase):
    '''Verify that the registeration process fails with respect
    to selecting an unavailable username and password confirmation'''

    @classmethod
    def setUpTestData(cls):
        User.objects.create_user(username="Python")
        cls.data = {
            'username': "Python",
            'password': "#secret#",
            'password2': "Secret"
        }
        cls.error_messages = [
            "Choose a different username", "Password confirmation failed"
        ]
        cls.serializer = UserRegisterationSerializer(data=cls.data)

    def test_user_registeration_invalid_confirmation(self):
        self.serializer.is_valid()
        print(self.serializer.errors)

import re

from django.contrib.auth.models import User

from rest_framework import serializers

class UsernameSerializer(serializers.ModelSerializer):
    username = serializers.SlugField(min_length=4, max_length=12)

    def validate_username(self, value):
        try:
            self.Meta.model.objects.get(username__iexact=value)
        except self.Meta.model.DoesNotExist:
            return value
        raise serializers.ValidationError("Choose a different username")

    class Meta:
        fields = ['username', ]
        model = User

class LoginSerializer(UsernameSerializer):
    password = serializers.RegexField(
        r"[0-9A-Za-z]+", min_length=5, max_length=8
    )

    def validate(self, data):
        username, password = [
            input.lower() for input in [data['username'], data['password']]
        ]
        if all(password[i] == password[i + 1] for i in range(len(password) - 1)) or username == password:
            raise serializers.ValidationError({
                'password': "Invalid password"
            })
        return data

    class Meta:
        fields = ['username', 'password', ]
        model = User

class UserRegistrationSerializer(LoginSerializer):
    password2 = serializers.RegexField(
        r"[0-9A-Za-z]+", min_length=5, max_length=8, write_only=True
    )

    def validate(self, data):
        data = super().validate(data)
        if data['password'] != data['password2']:
            raise serializers.ValidationError({"password2": "Password confirmation failed"})
        return data

    class Meta:
        model = User
        fields = ['username', 'password', 'password2']