I think I should change this test too, it's really testing that the matcher doesn't use the same value twice for primary keys, would the following change be ok?

```
it 'does not use default values for primary keys` do
  model_1 = ... 
  model_2 = ...
  expect(model_1).to matcher
  expect { expect(model_2).to matcher }.not_to_raise error 
end
```