Adds all_pks() method and test.

tests/test_json_model.py

@@ -186,6 +186,35 @@ async def test_saves_model_and_creates_pk(address, m, redis):
     assert member2 == member
     assert member2.address == address
 
+@pytest.mark.asyncio
+async def test_all_pks(address, m, redis):
+    member = m.Member(
+        first_name="Andrew",
+        last_name="Brookins",
+        email="a@example.com",
+        join_date=today,
+        age=38,
+        address=address,
+    )
+
+    await member.save()  
+
+    member1 = m.Member(
+        first_name="Simon",
+        last_name="Prickett",
+        email="s@example.com",
+        join_date=today,
+        age=99,
+        address=address,
+    )
+
+    await member1.save()
+
+    pk_list = []
+    async for pk in await m.Member.all_pks():
+        pk_list.append(pk)
+
+    assert len(pk_list) == 2
 
 @pytest.mark.asyncio
 async def test_delete(address, m, redis):