That would be irritating, because:
```
lib/tasks/export.rake
50:    exporter = Whitehall::Exporters::RedirectorDocumentMappings.new(Rails.env)
```
Rails.env is never 'preview', which is I think why these tests originally had such a mix of 'test.alphagov.co.uk' and 'preview.alphagov.co.uk' in their expectations and magic switching on ENV'FACTER_govuk_platform'].

Also I'm not convinced that the platform should have any relation to the domain name - I might want to call my platform new_staging, but have a domainname of awesomesauce.co.uk and I think I should actually be allowed to specify that with the correct environment variables.