Add unit tests for poller package

[Shaddoll]

What changed?
Add unit tests for poller package

Why?
improve coverage

How did you test it?
unit tests

Potential risks

Release notes

Documentation Changes

[taylanisikdemir]

nit: Less indentation is preferred so I don't favor grouping structs under a type( ... ) section

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.39%. Comparing base (4326afb) to head (c751586).
Report is 6 commits behind head on master.

Additional details and impacted files

Files	Coverage Δ
service/matching/poller/history.go	100.00% <ø> (ø)

... and 9 files with indirect coverage changes

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[coveralls]

Pull Request Test Coverage Report for Build 018fea05-88b4-4991-90c9-851efe00e9f8

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 111 unchanged lines in 11 files lost coverage.
• Overall coverage decreased (-0.05%) to 70.687%

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Files with Coverage Reduction	New Missed Lines	%
service/matching/tasklist/db.go	2	73.23%
common/peerprovider/ringpopprovider/config.go	2	81.58%
service/matching/tasklist/task_list_manager.go	2	76.48%
common/persistence/sql/sqlplugin/mysql/task.go	2	73.68%
service/matching/tasklist/matcher.go	2	89.35%
common/persistence/sql/sqlplugin/mysql/db.go	2	79.49%
common/log/tag/tags.go	3	50.46%
common/task/fifo_task_scheduler.go	3	84.54%
bench/lib/client.go	4	0.0%
service/matching/tasklist/task_reader.go	11	75.33%

Totals
Change from base Build 018fe9e9-5b1b-4b55-a4a1-8f985d11d2a5:	-0.05%
Covered Lines:	105289
Relevant Lines:	148951

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💛 - Coveralls