MustLoadListingFixture - load listing json from fixtures.

MustNewPeerIDProtobuf returns a PeerID protobuf example that is known to be valid.

NewValidPeerInfo returns a PeerInfo example that is known to be valid.

NewCryptoListing - return new crypto listing.

NewListing - return new pb.Listing.

NewListingWithShippingRegions - return new listing with shipping region.