351.5.

yammer:messages?[options]

from("direct:start")
    .to("yammer:messages?consumerKey=aConsumerKey&consumerSecret=aConsumerSecretKey&accessToken=aAccessToken")
    .to("mock:result");

template.sendBody("direct:start", "Hi from Camel!");

Exchange exchange = mock.getExchanges().get(0);
Messages messages = exchange.getIn().getBody(Messages.class);

assertEquals(1, messages.getMessages().size());
assertEquals("Hi from Camel!", messages.getMessages().get(0).getBody().getPlain());