Django REST API test returns HTTP_200_OK when requesting users-list but HTTP_404_NOT_FOUND for users-details

I'm trying to write tests for a UserViewSet:

users.models.py

class User(AbstractUser):

users.serializers.py

class UserSerializer(serializers.ModelSerializer):

    email = serializers.EmailField(
            write_only=True,
            required=True,
            min_length=8,
            validators=[UniqueValidator(queryset=User.objects.all())]
            )

    username = serializers.CharField(
            max_length=32,
            required=True,
            validators=[UniqueValidator(queryset=User.objects.all())]
            )

    class Meta:
        model = User
        fields = (
            'id',
            'first_name',
            'last_name',
            'username',
            'password',
            'email',
        )

        extra_kwargs = {
            'password': {'write_only': True, 'min_length':8,'required':True},
        }

users.views.py

class UserViewSet(viewsets.ModelViewSet):
    queryset = User.objects.all()
    serializer_class = serializers.UserSerializer
    permission_classes = [permissions.IsAuthenticated]

users.tests.py

def setup_user(username='test_user', email='test_user@test.com',password='test_password'):
    test_user = User.objects.create_user(username=username, email=email,password=password)
    test_user.save()
    return test_user

class UserTest(APITestCase):
    def setUp(self):
        self.test_user = setup_user()
        self.test_user2 = setup_user(username='test_user2', email='test_user2@test.com',password='test_password2')

    # test the /users/ endpoint
    def test_authenticated_user_can_get_users_list(self):
        self.client.force_authenticate(user=self.test_user)
        response = self.client.get(reverse('users-list'), format='json')
        self.assertEqual(response.status_code,status.HTTP_200_OK)


    def test_authenticated_user_can_get_users_detail(self):
        self.client.force_authenticate(user=self.test_user)
        user_detail_url = reverse('users-detail', args=(1,))
        print(user_detail_url)
        response = self.client.get(user_detail_url, format='json')
        print(response)

The first test runs fine and returns a HTTP_200_OK status code as I expect. However the response for the detail view returns a HTTP_404_NOT_FOUND which I don't understand since everything seems to work fine outside of this test:

If I run python manage.py runserver and check the /api/users/:id/ endpoint everything works as expected and the corresponding user is correctly serialized. Same if I use requests and request any user details:

r = requests.get('{}/users/2/'.format(api_root),  headers={'Authorization': 'Token {}'.format(get_token())})

(and yeah I'm using Token Authentication) I see all the fields I expect to see in r.json():

id, first_name, last_name and username

thanks for your help!