add testing of request body

Author: kenichi

test/web_push_test.exs

@@ -19,6 +19,14 @@ defmodule WebPushTest do
       assert Map.get(request.headers, "Urgency") == "normal"
 
       assert request.body == WebPush.decode(expected())
+
+      <<salt::binary-size(16), rs::unsigned-big-integer-size(32), idlen::8,
+        keyid::binary-size(idlen), _ciphertext::binary>> = request.body
+
+      assert salt == salt()
+      assert rs == 4096
+      assert idlen == 65
+      assert keyid == elem(as_key_pair(), 0)
     end
   end