[History Server] Add unit tests for uncovered pure functions

[win5923]

Description

Increase History Server test coverage by adding unit tests for pure functions.

Each item should be a small, self-contained change consisting primarily of a add or extend _test.go file with table-driven test cases. No production code changes are expected.

Reproducing the numbers

Measured on master @ eed5b24:

cd historyserver
go test -coverprofile=cover.out ./pkg/... ./cmd/...

# total
go tool cover -func=cover.out | tail -1
# -> total:  (statements)  40.6%

# line-level HTML report, useful for picking the branches worth pinning
go tool cover -html=cover.out

Current coverage by package

Package	Coverage
pkg/storage/clustermetadata	97.9%
pkg/storage/clusterlogs	96.6%
pkg/eventserver	64.3%
pkg/collector/eventcollector	62.6%
pkg/compression	62.1%
pkg/storage/gcs	59.8%
pkg/collector/logcollector	40.2%
pkg/historyserver	39.5%
pkg/eventserver/types	29.7%
pkg/utils	27.1%
pkg/storage/s3	0.0%
pkg/storage/azureblob	0.0%
pkg/storage/aliyunoss/ray	0.0%
total	40.6%

Files that need test cases

Each item is independent.

• 1. pkg/utils/tasksummary.go — 0.0% [History Server][CI] add unit tests for the lineage task summary #5128
• 2. pkg/eventserver/types/task.go — 0.0% @markwu7
• 3. pkg/historyserver/timeline.go — 0.0% @AlterHoodie
• 4. pkg/utils/filter.go — 0.0% @wuallen57730
• 5. pkg/historyserver/cluster_status.go — 47.4% @jinbum-kim
• 6. pkg/utils/utils.go — 61.9%
• 7. pkg/eventserver/state_transition.go — 0.0%

[AlterHoodie]

@win5923 can I get this assigned? will look into it and draft a PR with test coverage results.

[win5923]

Yes, you can pick one first.

[AlterHoodie]

Sorry didn't notice each item is independent, will pick 3

[jinbum-kim]

Hi @win5923 I'd like to work on 5(pkg/historyserver/cluster_status.go). Would it be okay to take this one?

[wuallen57730]

Hi @win5923, may I take 4(pkg/utils/filter.go)?

[markwu7]

I can help the second one pkg/eventserver/types/task.go

[hysuuuu]

Hi @win5923, can I take 7. pkg/eventserver/state_transition.go?