More tests with examples

[LiXizhi]

No description provided.

[liuluheng]

when test for throuput, the loop for replicating logs to the followers is often the cause for node lagging down. The latter node in the loop(only 2 nodes) always lags down. But the function called in the loop is async and should not be the reason for this(loop can be finished in one tick). Through the log, we can see the former node's rsp arrive ealier to the leader and leader can not handle as quickly as the message arrives.