public KafkaSource topic(String topic) {
		Assert.hasText(topic, "topic must not be empty nor null");
		this.topic = topic;
		return this;
	}
sets the topic for the kafka source

@param topic the topic that data will be posted.
@return instance of the KafkaSource
spring-xd-test-fixtures/src/main/java/org/springframework/xd/test/fixtures/KafkaSource.java