Some test cases are failing because Port bind issue.

very frequently testcases are failing because of :

java.net.BindException: Address already in use
at sun.nio.ch.Net.bind(Native Method)
at sun.nio.ch.ServerSocketChannelImpl.bind(ServerSocketChannelImpl.java:126)
at sun.nio.ch.ServerSocketAdaptor.bind(ServerSocketAdaptor.java:59)
at sun.nio.ch.ServerSocketAdaptor.bind(ServerSocketAdaptor.java:52)
at org.apache.zookeeper.server.NIOServerCnxnFactory.configure(NIOServerCnxnFactory.java:111)
at org.apache.zookeeper.server.ServerCnxnFactory.createFactory(ServerCnxnFactory.java:112)
at org.apache.zookeeper.server.quorum.QuorumPeer.<init>(QuorumPeer.java:514)
at org.apache.zookeeper.test.QuorumBase.startServers(QuorumBase.java:156)
at org.apache.zookeeper.test.QuorumBase.setUp(QuorumBase.java:103)
at org.apache.zookeeper.test.QuorumBase.setUp(QuorumBase.java:67)

may be because of Port Assignment so please give me some suggestions if someone is also facing same problem.