For example:

java.lang.RuntimeException: "JBAS010839: Operation failed or was rolled back on all servers."
at org.jboss.as.test.integration.domain.management.util.DomainLifecycleUtil.executeForResult(DomainLifecycleUtil.java:582)
at org.jboss.as.test.integration.domain.DomainControllerMigrationTestCase.testDCFailover(DomainControllerMigrationTestCase.java:206)

With this in the logs:

[Host Controller] 14:51:08,996 INFO [org.jboss.as] (Controller Boot Thread) JBAS015874: JBoss EAP 6.2.0.Alpha1 (AS 7.3.0.Final-redhat-SNAPSHOT) (Host Controller) started in 829ms - Started 12 of 12 services (0 services are passive or on-demand)
[Server:failover-two] 14:51:10,113 INFO [org.jboss.as.server.deployment] (MSC service thread 1-2) JBAS015876: Starting deployment of "SimpleServlet.war" (runtime-name: "SimpleServlet.war")
[Host Controller] 14:51:10,377 INFO [org.jboss.as.domain.controller.mgmt] (Remoting "failover-h3:MANAGEMENT" task-2) JBAS010920: Server [Server:failover-three] registered using connection [Channel ID 7e979de4 (inbound) of Remoting connection 00429bb7 to /127.0.0.1:53634]
[Host Controller] 14:51:11,185 ERROR [org.jboss.as.controller.management-operation] (domain-connection-threads - 2) JBAS014612: Operation ("composite") failed - address: ([
[Host Controller] ("host" => "failover-h3"),
[Host Controller] ("server" => "failover-three")
[Host Controller] ]): java.lang.RuntimeException: java.io.IOException: JBAS012175: Channel closed
[Host Controller] at org.jboss.as.controller.remote.RemoteProxyController.execute(RemoteProxyController.java:203) [jboss-as-controller-7.3.0.Final-redhat-SNAPSHOT.jar:7.3.0.Final-redhat-SNAPSHOT]
[Host Controller] at org.jboss.as.controller.TransformingProxyController$TransformingProxyControllerImpl.execute(TransformingProxyController.java:149) [jboss-as-controller-7.3.0.Final-redhat-SNAPSHOT.jar:7.3.0.Final-redhat-SNAPSHOT]
[Host Controller] at org.jboss.as.controller.ProxyStepHandler.execute(ProxyStepHandler.java:130) [jboss-as-controller-7.3.0.Final-redhat-SNAPSHOT.jar:7.3.0.Final-redhat-SNAPSHOT]
[Host Controller] at org.jboss.as.controller.AbstractOperationContext.executeStep(AbstractOperationContext.java:624) [jboss-as-controller-7.3.0.Final-redhat-SNAPSHOT.jar:7.3.0.Final-redhat-SNAPSHOT]
.....
[Host Controller] Caused by: java.io.IOException: JBAS012175: Channel closed
[Host Controller] at org.jboss.as.host.controller.ManagedServerProxy$DisconnectedProtocolClient.execute(ManagedServerProxy.java:114)
[Host Controller] at org.jboss.as.host.controller.ManagedServerProxy.execute(ManagedServerProxy.java:92)
[Host Controller] at org.jboss.as.host.controller.ManagedServerProxy.execute(ManagedServerProxy.java:80)
[Host Controller] at org.jboss.as.controller.remote.RemoteProxyController.execute(RemoteProxyController.java:159) [jboss-as-controller-7.3.0.Final-redhat-SNAPSHOT.jar:7.3.0.Final-redhat-SNAPSHOT]
[Host Controller] ... 23 more

I believe what is going on here is the test is hitting expected behavior. It restarts an HC without restarting the servers. When the HC is reloaded, it is aware that it has disconnected servers. While it awaits reconnect, any attempt to send an op through to the disconnected server will get the exception above.

If my analysis is correct, then the test just needs adjusting to check server status before continuing on. If it's incorrect and this shouldn't fail, then we have a bug. A 3rd option is it's correct, but the behavior is bad.