Update impression_test.go

Author: CarolynU

impression_test.go

@@ -1,5 +1,10 @@
 package openrtb
 
+import (
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+)
+
 var _ = Describe("Impression", func() {
 	var subject *Impression