Django test: TransactionManagementError: you cannot execute queries until the end of an atomic block

Django newbie here. I am trying to implement unit tests for a simple API that I have developed. Below you can find my test implementation that works great:

from django.test import TestCase
from my_app.models import MyModel


class TestMyViewSet(TestCase):
    """
    Unit tests for endpoints in MyViewSet.
    """
    fixtures = ['my_app/fixtures/data.yaml']

    def setUp(self):
        # Making setup for the test case here.


    def test_post_my_resource(self):

        # Checking that fixture is loaded correctly.
        self.assertEqual(MyModel.objects.all().count(),1)

        request_body = {
            'my_resource': "input_for_my_resource"
        }

        response = self.client.post('/my_resources/', data=request_body)
        self.assertEqual(response.status_code, 201)
        # self.assertEqual(MyModel.objects.all().count(),2)

      

        
        
        
      

    

But when I removed the last line self.assertEqual(MyModel.objects.all().count(),2)

from the comment to verify that it was my_resource

successfully created in the corresponding model by checking the number of instances, I got the error:

TransactionManagementError: An error occurred in the current transaction. You cannot execute queries until the end of the atomic block.

What am I missing here?

Thanks in advance!

PS: I come across the following question: TransactionManagementError "You cannot execute queries to the end of the atomic block when using signals, but only during unit testing, but I'm not sure what happens the same in my case.