Added BaseDatabaseSchemaEditor._effective_default() to allow testing without a connection.

django/db/backends/base/schema.py

@@ -199,8 +199,9 @@ class BaseDatabaseSchemaEditor:
             'requires_literal_defaults must provide a prepare_default() method'
         )
 
-    def effective_default(self, field):
-        """Return a field's effective database default value."""
+    @classmethod
+    def _effective_default(self, field):
+        # This method allows testing its logic without a connection.
         if field.has_default():
             default = field.get_default()
         elif not field.null and field.blank and field.empty_strings_allowed:
@@ -219,8 +220,11 @@ class BaseDatabaseSchemaEditor:
                 default = timezone.now()
         else:
             default = None
-        # Convert the value so it can be sent to the database.
-        return field.get_db_prep_save(default, self.connection)
+        return default
+
+    def effective_default(self, field):
+        """Return a field's effective database default value."""
+        return field.get_db_prep_save(self._effective_default(field), self.connection)
 
     def quote_value(self, value):
         """

tests/backends/base/test_schema.py

@@ -1,8 +1,9 @@
-from django.db import connection, models
-from django.test import TestCase
+from django.db import models
+from django.db.backends.base.schema import BaseDatabaseSchemaEditor
+from django.test import SimpleTestCase
 
 
-class SchemaEditorTests(TestCase):
+class SchemaEditorTests(SimpleTestCase):
 
     def test_effective_default_callable(self):
         """SchemaEditor.effective_default() shouldn't call callable defaults."""
@@ -14,9 +15,5 @@ class SchemaEditorTests(TestCase):
             def _get_default(self):
                 return self.default
 
-            def get_db_prep_save(self, default, connection):
-                return default
-
         field = MyCharField(max_length=1, default=MyStr)
-        with connection.schema_editor() as editor:
-            self.assertEqual(editor.effective_default(field), MyStr)
+        self.assertEqual(BaseDatabaseSchemaEditor._effective_default(field), MyStr)