Due to a bug, a recv topic, if given, was not considered correctly.
In some cases, a match could result from a message with a topic not
equal to the given topic. The current code fixes that bug. If you
have a test that now fails and didn't previously, check if you are
specifying a topic for each recv. In those cases, either adjust the
topic or remove the topic specification and check the message topic in
a guard (via msg, which has a value like
{"topic":TOPIC,"payload":PAYLOAD}).