Add more unit tests for OS client

[neil-xie]

What changed?
Add more unit tests for OS client

Why?
Improve test coverage

How did you test it?

Potential risks

Release notes

Documentation Changes

[coveralls]

Pull Request Test Coverage Report for Build 018e9f90-de56-44a6-8a9f-5f54421157dc

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 51 unchanged lines in 14 files lost coverage.
• Overall coverage increased (+0.1%) to 65.545%

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Files with Coverage Reduction	New Missed Lines	%
service/history/queue/timer_queue_processor_base.go	1	77.62%
service/history/task/transfer_standby_task_executor.go	2	86.6%
common/task/weighted_round_robin_task_scheduler.go	2	88.06%
common/peerprovider/ringpopprovider/config.go	2	81.58%
service/matching/db.go	2	73.23%
common/util.go	2	91.78%
service/history/task/fetcher.go	2	85.05%
common/persistence/historyManager.go	2	66.67%
common/log/tag/tags.go	3	50.18%
common/task/fifo_task_scheduler.go	3	82.47%

Totals
Change from base Build 018e9d58-6c4d-48f3-914d-eb330d0c7d63:	0.1%
Covered Lines:	95918
Relevant Lines:	146339

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💛 - Coveralls