text: Title: Replace Powermock with Mockito
  Body: **Summary**
  
  - Powermock seems no longer maintained https://github.com/powermock/powermock/issues/1117 where the last commit on the master was in 2020
  - Using Powermock with Java 11 causing excessive amount of "An illegal reflective access operation has occurred" warnings https://github.com/powermock/powermock/issues/969
  
  This issue is asking to replace Powermock (mostly used for mocking static method and whiteboxing to access private method) with Mockito equivalent.
  
  **Urgency**
  
  Low