Enable/fix Spotbugs on test classes

[conniey]

Fix spotbug issues in test classes. Then we can set <includeTests>true</includeTests> rather than false in pom.xml.

[shreelakshmijoshi]

Hi @conniey !
I am a new open source contributor and would like to solve this issue, could you help me understand the issue better by providing some extra references ?
Is this is issue open to contribute ?