update error handling in tcp call hander

tcp-connection_test.go

@@ -21,7 +21,7 @@ func TestGenericConnection(t *testing.T) {
 		return nil
 	})
 	listener.AddHandler(3, func(input *FrameWithPayload, resultChan chan<- FrameWithPayload) error {
-		return fmt.Errorf("Error")
+		return fmt.Errorf("Error in custom handler")
 	})
 	r, err := conn.Call(1, datta)
 	if err != nil {