Added additional unit tests testing history handler

[timl3136]

What changed?
Add unit tests for history handler

Why?
Improve test coverage

How did you test it?
Unit tests

Potential risks

Release notes

Documentation Changes

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 66.07%. Comparing base (b4a1f04) to head (f2ee9d7).
Report is 2 commits behind head on master.

Additional details and impacted files

see 8 files with indirect coverage changes

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[coveralls]

Pull Request Test Coverage Report for Build 018f5f90-8e60-435b-8a24-c47a85b01ec7

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 75 unchanged lines in 7 files lost coverage.
• Overall coverage increased (+0.08%) to 68.894%

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Files with Coverage Reduction	New Missed Lines	%
common/task/weighted_round_robin_task_scheduler.go	1	89.05%
common/membership/hashring.go	2	84.69%
common/persistence/statsComputer.go	3	96.79%
common/task/fifo_task_scheduler.go	4	83.51%
service/frontend/api/handler.go	4	62.2%
service/history/engine/engineimpl/poll_mutable_state.go	9	74.16%
service/history/replication/task_processor.go	52	78.81%

Totals
Change from base Build 018f5e8f-a247-406e-9920-f997ba145d18:	0.08%
Covered Lines:	101213
Relevant Lines:	146912

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💛 - Coveralls