Refs #373 -- Added Model._is_pk_set() abstraction to check if a Model's PK is set.

tests/basic/tests.py

@@ -661,6 +661,31 @@ class ModelTest(TestCase):
             headline__startswith="Area",
         )
 
+    def test_is_pk_unset(self):
+        cases = [
+            Article(),
+            Article(id=None),
+        ]
+        for case in cases:
+            with self.subTest(case=case):
+                self.assertIs(case._is_pk_set(), False)
+
+    def test_is_pk_set(self):
+        def new_instance():
+            a = Article(pub_date=datetime.today())
+            a.save()
+            return a
+
+        cases = [
+            Article(id=1),
+            Article(id=0),
+            Article.objects.create(pub_date=datetime.today()),
+            new_instance(),
+        ]
+        for case in cases:
+            with self.subTest(case=case):
+                self.assertIs(case._is_pk_set(), True)
+
 
 class ModelLookupTest(TestCase):
     @classmethod