Add test for ES v6 client Search method

[neil-xie]

What changed?
Add unit test for Search method

Why?
Increase test coverage

How did you test it?

Potential risks

Release notes

Documentation Changes

[codecov]

Codecov Report

Merging #5727 (886a0fd) into master (71a196c) will increase coverage by 0.02%.
The diff coverage is n/a.

Additional details and impacted files

see 7 files with indirect coverage changes

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[coveralls]

Pull Request Test Coverage Report for Build 018e12f0-6cf0-4300-9145-49f9d3156bd9

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 48 unchanged lines in 11 files lost coverage.
• Overall coverage increased (+0.04%) to 63.324%

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Files with Coverage Reduction	New Missed Lines	%
common/membership/hashring.go	2	82.23%
common/persistence/historyManager.go	2	66.67%
service/history/execution/mutable_state_util.go	2	78.48%
service/history/shard/context.go	2	66.67%
service/matching/taskListManager.go	2	80.96%
common/persistence/nosql/nosqlplugin/cassandra/workflow.go	3	63.03%
service/history/task/fetcher.go	4	86.08%
service/history/task/transfer_standby_task_executor.go	4	85.77%
service/frontend/api/handler.go	5	62.23%
common/persistence/sql/workflowStateMaps.go	8	81.25%

Totals
Change from base Build 018e12b3-d0a9-4a57-9f85-00623526ab6b:	0.04%
Covered Lines:	92886
Relevant Lines:	146684

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💛 - Coveralls