text: from django.db import models
  from django.db.backends.base.schema import BaseDatabaseSchemaEditor
  from django.test import SimpleTestCase
  
  
  class SchemaEditorTests(SimpleTestCase):
  
      def test_effective_default_callable(self):
          """SchemaEditor.effective_default() shouldn't call callable defaults."""
          class MyStr(str):
              def __call__(self):
                  return self
  
          class MyCharField(models.CharField):
              def _get_default(self):
                  return self.default
  
          field = MyCharField(max_length=1, default=MyStr)
          self.assertEqual(BaseDatabaseSchemaEditor._effective_default(field), MyStr)
  