Add unit tests for functions in gocql/batch.go

[timl3136]

What changed?
Add unit tests for functions in batch.go

Why?
Improve test coverage

How did you test it?
Unit tests

Potential risks

Release notes

Documentation Changes

[codecov]

Codecov Report

Merging #5759 (0f17107) into master (e198ca3) will decrease coverage by 0.09%.
The diff coverage is n/a.

Additional details and impacted files

see 10 files with indirect coverage changes

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[coveralls]

Pull Request Test Coverage Report for Build 018e1af7-5255-4606-b624-61804f88844e

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 111 unchanged lines in 20 files lost coverage.
• Overall coverage decreased (-0.06%) to 63.211%

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Files with Coverage Reduction	New Missed Lines	%
common/task/weighted_round_robin_task_scheduler.go	2	89.05%
common/task/fifo_task_scheduler.go	2	84.54%
service/matching/db.go	2	73.23%
service/history/task/transfer_active_task_executor.go	2	72.51%
common/persistence/sql/sqlplugin/mysql/db.go	2	79.49%
common/persistence/sql/common.go	2	46.75%
common/persistence/sql/sql_task_store.go	2	54.32%
common/persistence/sql/sqlplugin/mysql/task.go	2	73.68%
common/persistence/executionManager.go	2	78.59%
service/history/queue/timer_gate.go	3	95.83%

Totals
Change from base Build 018e1af5-7c55-428d-9cce-978e3813e7da:	-0.06%
Covered Lines:	92667
Relevant Lines:	146599

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💛 - Coveralls