Could you please show the code you try?
Here is the simple example in iex shell:
iex(1)> Process.info(self, :message_queue_len)
{:message_queue_len, 0}
iex(2)> send(self, :hello)
:hello
iex(3)> Process.info(self, :message_queue_len)
{:message_queue_len, 1}
iex(4)> Process.info(self, :messages)
{:messages, [:hello]}
