Add tests and continue integration test

offer.go

@@ -0,0 +1,33 @@
+package ebay
+
+import (
+	"net/http"
+)
+
+// OfferService handles communication with the Offer API
+//
+// eBay API docs: https://developer.ebay.com/api-docs/buy/offer/static/overview.html
+type OfferService service
+
+// Valid marketplace IDs
+const (
+	BuyMarketplaceAustralia    = "EBAY_AU"
+	BuyMarketplaceCanada       = "EBAY_CA"
+	BuyMarketplaceGermany      = "EBAY_DE"
+	BuyMarketplaceSpain        = "EBAY_ES"
+	BuyMarketplaceFrance       = "EBAY_FR"
+	BuyMarketplaceGreatBritain = "EBAY_GB"
+	BuyMarketplaceHongKong     = "EBAY_HK"
+	BuyMarketplaceItalia       = "EBAY_IT"
+	BuyMarketplaceUSA          = "EBAY_US"
+)
+
+// OptBuyMarketplace adds the header containing the marketplace id:
+// https://developer.ebay.com/api-docs/buy/static/ref-marketplace-supported.html
+//
+// eBay API docs: https://developer.ebay.com/api-docs/buy/static/api-browse.html#Headers
+func OptBuyMarketplace(marketplaceID string) func(*http.Request) {
+	return func(req *http.Request) {
+		req.Header.Set("X-EBAY-C-MARKETPLACE-ID", marketplaceID)
+	}
+}