And mock the preference value, rather than setting it. Before, the set preference could have leaked to other tests.
(I noticed that it was already like this in product_import_spec.rb)
We still have the scale stored in two places but in our current system
that's part of a unit's "id".
If the DFC adds that value to its standard then we can use it for lookup
and don't need to repeat it.
* https://github.com/datafoodconsortium/taxonomies/issues/7
ie truncate 12.50001234 to 12.5
When using imperial, the scalling calculation rounding results in value unit
having extra decimal when converted back to imperial
+ related spec
