Add test for es v6 bulk processor

[neil-xie]

What changed?
Added unit test for bulk processor start, close, stop, add, flush methods
Added unit test for run bulk processor

Why?
Test coverage

How did you test it?
Unit test

Potential risks

Release notes

Documentation Changes

[coveralls]

Pull Request Test Coverage Report for Build 018e1b39-fd43-44ef-8b19-ba508c5e8d16

Details

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• 81 unchanged lines in 10 files lost coverage.
• Overall coverage increased (+0.02%) to 63.251%

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Files with Coverage Reduction	New Missed Lines	%
common/task/fifo_task_scheduler.go	2	87.63%
service/history/task/transfer_active_task_executor.go	2	72.38%
common/persistence/statsComputer.go	2	95.71%
service/history/task/fetcher.go	2	85.05%
common/persistence/executionManager.go	2	78.59%
service/history/task/cross_cluster_task_processor.go	8	80.79%
service/history/shard/context.go	9	66.84%
service/history/execution/context.go	14	68.05%
common/persistence/sql/sql_execution_store.go	16	63.57%
service/history/task/task_util.go	24	69.43%

Totals
Change from base Build 018e1b39-db6b-450f-be5c-e6030346d786:	0.02%
Covered Lines:	92725
Relevant Lines:	146598

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💛 - Coveralls