Test coverage

[ayush0407]

What's the purpose of this PR

Increases the test coverage.

XXXXX

Which issue(s) this PR fixes:

Fixes #3874

Brief changelog

XXXXX

Follow this checklist to help us incorporate your contribution quickly and easily:

• Read the Contributing Guide before making this pull request.
• Write a pull request description that is detailed enough to understand what the pull request does, how, and why.
• Write necessary unit tests to verify the code.
• Run mvn clean test to make sure this pull request doesn't break anything.
• Update the CHANGES log.

[codecov-commenter]

Codecov Report

Merging #4292 (39622d8) into master (f6ce7f5) will increase coverage by 0.53%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #4292      +/-   ##
============================================
+ Coverage     53.14%   53.67%   +0.53%     
- Complexity     2668     2702      +34     
============================================
  Files           488      488              
  Lines         15253    15253              
  Branches       1577     1577              
============================================
+ Hits           8106     8187      +81     
+ Misses         6592     6510      -82     
- Partials        555      556       +1     

Impacted Files	Coverage Δ
.../apollo/internals/RemoteConfigLongPollService.java	77.10% <0.00%> (-1.21%)	⬇️
...ervice/service/ReleaseMessageServiceWithCache.java	85.88% <0.00%> (-1.18%)	⬇️
...framework/apollo/portal/entity/bo/NamespaceBO.java	72.41% <0.00%> (+3.44%)	⬆️
...ip/framework/apollo/core/utils/PropertiesUtil.java	92.30% <0.00%> (+15.38%)	⬆️
...ctrip/framework/apollo/core/utils/MachineUtil.java	80.00% <0.00%> (+80.00%)	⬆️
...ramework/apollo/openapi/util/OpenApiBeanUtils.java	98.52% <0.00%> (+89.70%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update f6ce7f5...39622d8. Read the comment docs.