TestNameNodeMXBean#testNameNodeMXBeanInfo expects a none-zero nonDFS size. The nonDFS size is defined as:
The space that is not used by HDFS. For instance, once you format a new disk to ext4, certain space is used for "lost-and-found" directory and ext4 metadata.
It will be possible to fully allocate all spaces in a filesystem for DFS use. In which case the nonDFS size will be zero. We can relax the check in the test to account for this case.