Add additional tests for ExecutionManager

[3vilhamster]

What changed?
Adding more tests to ExecutionManager.
Now covering GetExecutionInfo and UpdateExecution.
That includes a lot of deserialization and data conversion. I've added some sane checks, if we'll spot any missing fields, it should be easy enough extend the test with extra fields.

Why?
Improving code coverage.

How did you test it?
unit tests

Potential risks

Release notes

Documentation Changes

[coveralls]

Pull Request Test Coverage Report for Build 018e759f-f52b-4536-86e5-067b10a27c55

Details

• 3 of 3 (100.0%) changed or added relevant lines in 1 file are covered.
• 88 unchanged lines in 15 files lost coverage.
• Overall coverage decreased (-0.02%) to 65.187%

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Files with Coverage Reduction	New Missed Lines	%
common/task/weighted_round_robin_task_scheduler.go	1	88.06%
service/history/task/transfer_standby_task_executor.go	2	87.01%
service/history/shard/context.go	2	67.47%
service/matching/db.go	2	73.23%
common/persistence/historyManager.go	2	66.67%
common/log/tag/tags.go	3	50.18%
service/history/task/fetcher.go	3	85.57%
service/matching/taskListManager.go	4	80.46%
common/persistence/nosql/nosqlplugin/cassandra/tasks.go	4	76.09%
common/persistence/nosql/nosql_task_store.go	5	61.95%

Totals
Change from base Build 018e712c-b24b-4404-8d45-a837376600cf:	-0.02%
Covered Lines:	95238
Relevant Lines:	146099

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💛 - Coveralls

[codecov]

Codecov Report

Merging #5809 (8fcc005) into master (3498c59) will increase coverage by 0.37%.
The diff coverage is 100.00%.

Additional details and impacted files

Files	Coverage Δ
common/persistence/execution_manager.go	58.40% <100.00%> (+46.33%)	⬆️

... and 9 files with indirect coverage changes

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