Added additional unit tests for service/history/handler.go

[timl3136]

What changed?
Added unit tests for mutablestate and shard related handler methods

Why?
Improve test coverage and stability

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 64.62%. Comparing base (e194e5e) to head (18eaa57).
Report is 1 commits behind head on master.

Additional details and impacted files

see 7 files with indirect coverage changes

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[coveralls]

Pull Request Test Coverage Report for Build 018f5540-2135-4642-8f71-eecc9203eb85

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 34 unchanged lines in 10 files lost coverage.
• Overall coverage increased (+0.07%) to 68.482%

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Files with Coverage Reduction	New Missed Lines	%
tools/cli/admin_db_decode_thrift.go	1	71.79%
common/persistence/nosql/utils.go	2	60.0%
service/matching/taskListManager.go	2	80.65%
service/matching/matcher.go	2	91.41%
common/persistence/errors.go	3	25.0%
common/persistence/nosql/nosql_config_store.go	3	44.0%
common/persistence/statsComputer.go	3	96.07%
common/dynamicconfig/configstore/config_store_client.go	4	73.42%
service/history/task/fetcher.go	6	85.05%
service/history/task/cross_cluster_task_processor.go	8	80.79%

Totals
Change from base Build 018f5503-b802-40c5-bbeb-ebb54e6aab3d:	0.07%
Covered Lines:	100587
Relevant Lines:	146880

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💛 - Coveralls