Why not using a ``bulk_create`` here?  I may be a bit obsessed with performance, but I like when tests also are fast ;)
```python
self.objs = NullableIntegerArrayModel.objects.bulk_create([
    NullableIntegerArrayModel(field=[1]),
    NullableIntegerArrayModel(field=[2]),
    NullableIntegerArrayModel(field=[2, 3]),
    NullableIntegerArrayModel(field=[20, 30, 40]),
    NullableIntegerArrayModel(field=None),
])
```