@Override
    protected org.apache.hadoop.hbase.procedure2.StateMachineProcedure.Flow
      executeFromState(BasicProcedureEnv env, ServerCrashState state)
        throws ProcedureYieldException, InterruptedException {
      return null;
    }
Do-nothing SimpleMachineProcedure for checking its toString.
hbase-procedure/src/test/java/org/apache/hadoop/hbase/procedure2/TestProcedureToString.java