Moved unit test files inside same directory as test target

The unit tests were inside the `gateway/tests` directory which had no
effect to the coverage for `go test`. Therefore, moved the tests inside
the same directory as the test target.

Signed-off-by: Ken Fukuyama <kenfdev@gmail.com>

gateway/handlers/cors_test.go

@@ -0,0 +1,34 @@
+package handlers
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+type customHandler struct {
+}
+
+func (h customHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+}
+
+func Test_HeadersAdded(t *testing.T) {
+	rr := httptest.NewRecorder()
+	handler := customHandler{}
+	host := "store.openfaas.com"
+
+	decorated := DecorateWithCORS(handler, host)
+	request, _ := http.NewRequest(http.MethodGet, "/", nil)
+	decorated.ServeHTTP(rr, request)
+
+	actual := rr.Header().Get("Access-Control-Allow-Origin")
+	if actual != host {
+		t.Errorf("Access-Control-Allow-Origin: want: %s got: %s", host, actual)
+	}
+
+	actualMethods := rr.Header().Get("Access-Control-Allow-Methods")
+	if actualMethods != http.MethodGet {
+		t.Errorf("Access-Control-Allow-Methods: want: %s got: %s", http.MethodGet, actualMethods)
+	}
+
+}