diff --git a/Makefile b/Makefile
index e6d02c0..15f5d18 100644
--- a/Makefile
+++ b/Makefile
@@ -15,3 +15,6 @@ cover:
 		go test -v -coverprofile=playstore.txt -covermode=count ./playstore
 		cat playstore.txt | grep -v "mode: count" >> coverage.txt
 		rm playstore.txt
+		go test -v -coverprofile=amazon.txt -covermode=count ./amazon
+		cat amazon.txt | grep -v "mode: count" >> coverage.txt
+		rm amazon.txt
diff --git a/playstore/validator.go b/playstore/validator.go
index 5d8dda2..d68cc17 100644
--- a/playstore/validator.go
+++ b/playstore/validator.go
@@ -31,6 +31,9 @@ func SetTimeout(t time.Duration) {
 type IABClient interface {
 	VerifySubscription(string, string, string) (*androidpublisher.SubscriptionPurchase, error)
 	VerifyProduct(string, string, string) (*androidpublisher.ProductPurchase, error)
+	CancelSubscription(string, string, string) error
+	RefundSubscription(string, string, string) error
+	RevokeSubscription(string, string, string) error
 }
 
 // The Client type implements VerifySubscription method