More validation tests
More validation tests

With these tests all possible validation error messages (i.e. message keys) from the API are tested at least once.

RichardKnop/digitalmarketplace-api,RichardKnop/digitalmarketplace-api,alphagov/digitalmarketplace-api,mtekel/digitalmarketplace-api,mtekel/digitalmarketplace-api,RichardKnop/digitalmarketplace-api,RichardKnop/digitalmarketplace-api,alphagov/digitalmarketplace-api,alphagov/digitalmarketplace-api,mtekel/digitalmarketplace-api,mtekel/digitalmarketplace-api