tests for abstract/swappable model initialization

(cherry picked from commit 0fea8a4d92)

polymorphic/tests/__init__.py

@@ -400,6 +400,23 @@ class DateModel(PolymorphicModel):
     date = models.DateTimeField()
 
 
+# Define abstract and swappable (being swapped for SwappedModel) models
+# To test manager validation (should be skipped for such models)
+class AbstractModel(PolymorphicModel):
+    class Meta:
+        abstract = True
+
+
+class SwappableModel(AbstractModel):
+    class Meta:
+        swappable = 'POLYMORPHIC_TEST_SWAPPABLE'
+
+
+class SwappedModel(AbstractModel):
+    pass
+
+
+
 # Import tests
 from .test_admin import *
 from .test_orm import *