openx adapter: forward bid response currency in openx adapter if set

it was always set to the default USD before

adapters/openx/openx.go

@@ -169,6 +169,11 @@ func (a *OpenxAdapter) MakeBids(internalRequest *openrtb.BidRequest, externalReq
 
 	bidResponse := adapters.NewBidderResponseWithBidsCapacity(5)
 
+	// overrride default currency
+	if bidResp.Cur != "" {
+		bidResponse.Currency = bidResp.Cur
+	}
+
 	for _, sb := range bidResp.SeatBid {
 		for i := range sb.Bid {
 			bidResponse.Bids = append(bidResponse.Bids, &adapters.TypedBid{

adapters/openx/openx_test.go

@@ -1,11 +1,48 @@
 package openx
 
 import (
+	"encoding/json"
 	"testing"
 
+	"github.com/mxmCherry/openrtb"
+	"github.com/prebid/prebid-server/adapters"
 	"github.com/prebid/prebid-server/adapters/adapterstest"
+	"github.com/stretchr/testify/assert"
 )
 
 func TestJsonSamples(t *testing.T) {
 	adapterstest.RunJSONBidderTest(t, "openxtest", NewOpenxBidder("http://rtb.openx.net/prebid"))
 }
+
+func TestResponseWithCurrencies(t *testing.T) {
+	assertCurrencyInBidResponse(t, "USD", nil)
+
+	currency := "USD"
+	assertCurrencyInBidResponse(t, "USD", &currency)
+
+	currency = "EUR"
+	assertCurrencyInBidResponse(t, "EUR", &currency)
+}
+
+func assertCurrencyInBidResponse(t *testing.T, expectedCurrency string, currency *string) {
+
+	bidder := NewOpenxBidder("http://rtb.openx.net/prebid")
+	prebidRequest := &openrtb.BidRequest{
+		Imp: []openrtb.Imp{},
+	}
+	mockedBidResponse := &openrtb.BidResponse{}
+	if currency != nil {
+		mockedBidResponse.Cur = *currency
+	}
+	body, _ := json.Marshal(mockedBidResponse)
+	responseData := &adapters.ResponseData{
+		StatusCode: 200,
+		Body:       body,
+	}
+	bidResponse, errs := bidder.MakeBids(prebidRequest, nil, responseData)
+
+	if errs != nil {
+		t.Fatalf("Failed to make bids %v", errs)
+	}
+	assert.Equal(t, expectedCurrency, bidResponse.Currency)
+}