test(workflow-operator): add unit test coverage for OperatorDescriptorUtils + DistributedAggregation + URLFetchUtil

[aglinxinyuan]

What changes were proposed in this PR?

Pin behavior of three small utility classes/objects in common/workflow-operator/. Each one is too thin to justify its own PR but cohesive as a bundle (utility surface). No production-code changes.

Spec	Source class	Tests
OperatorDescriptorUtilsSpec	OperatorDescriptorUtils (object)	8
DistributedAggregationSpec	DistributedAggregation (case class)	9
URLFetchUtilSpec	URLFetchUtil (object)	6

All three spec files follow the <srcClassName>Spec.scala one-to-one convention.

Behavior pinned — OperatorDescriptorUtils

Surface	Contract
equallyPartitionGoal size	result has exactly totalNumWorkers slots
Sum invariant	slots sum back to goal across goal ∈ [0..20] × workers ∈ [1..5]
Even partition	when goal % workers == 0, every slot is goal / workers
Remainder placement	the first goal % workers slots get +1 (in order)
goal < workers edge case	first goal slots get 1, the rest get 0
toImmutableMap empty	empty java.util.Map → empty Scala Map
toImmutableMap preserves entries	round-trip preserves every key/value pair
Return type	static type is scala.collection.immutable.Map (compile-time enforced)

Behavior pinned — DistributedAggregation

Surface	Contract
Case-class shape	all four function members reachable; equality on identical function refs
init	produces the zero partial (0L, 0L)
iterate	folds one tuple in: sum += value, count += 1
merge	adds two partials componentwise
finalAgg divides	(15L, 5L) → 3.0d
finalAgg zero guard	(0L, 0L) → 0.0d (no divide-by-zero)
End-to-end single-node	average of 1..5 via fold-left == 3.0
End-to-end with merge	same answer via two partial nodes + merge

Behavior pinned — URLFetchUtil

Surface	Contract
Success path	getInputStreamFromURL(file:tempFile) returns Some(stream) carrying the file's exact bytes
Success with explicit retries	same, with retries = 3
Failure path (default retries)	non-existent file: URL returns None
Failure path (retries = 0)	loop iterates zero times → None immediately
Failure path (retries = 2)	persistent failure exhausts retries → None
Default arg value	getInputStreamFromURL\$default\$2 == 5, verified via Scala's synthetic default-accessor

The URLFetchUtil specs use the JVM's built-in file: URL handler against temporary files (success path) and non-existent paths (failure path) — no external network calls or process exec.

Any related issues, documentation, discussions?

Closes #5795.

How was this PR tested?

Pure unit-test additions; verified locally with:

• sbt \"WorkflowOperator/testOnly org.apache.texera.amber.operator.util.OperatorDescriptorUtilsSpec org.apache.texera.amber.operator.aggregate.DistributedAggregationSpec org.apache.texera.amber.operator.source.fetcher.URLFetchUtilSpec\" — 23 tests, all green
• sbt \"WorkflowOperator/Test/scalafmtCheck\" — clean
• CI to confirm

Was this PR authored or co-authored using generative AI tooling?

Generated-by: Claude Code (Opus 4.7 [1M context])

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 53.27%. Comparing base (731d671) to head (c1b3d29).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #5798      +/-   ##
============================================
- Coverage     53.30%   53.27%   -0.04%     
+ Complexity     2668     2663       -5     
============================================
  Files          1098     1098              
  Lines         42532    42532              
  Branches       4575     4575              
============================================
- Hits          22673    22659      -14     
- Misses        18530    18539       +9     
- Partials       1329     1334       +5     

Flag	Coverage Δ		*Carryforward flag
access-control-service	70.44% <ø> (ø)
agent-service	34.36% <ø> (ø)		Carriedforward from b6d2502
amber	53.72% <ø> (-0.09%)	⬇️
computing-unit-managing-service	1.65% <ø> (ø)
config-service	56.71% <ø> (ø)
file-service	57.06% <ø> (ø)
frontend	48.00% <ø> (ø)		Carriedforward from b6d2502
pyamber	90.13% <ø> (ø)		Carriedforward from b6d2502
python	90.80% <ø> (ø)		Carriedforward from b6d2502
workflow-compiling-service	58.69% <ø> (ø)

*This pull request uses carry forward flags. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[Copilot]

Pull request overview

Adds Scala unit-test coverage for three small utility surfaces in common/workflow-operator/, aiming to pin existing behavior without modifying production code.

Changes:

• Add OperatorDescriptorUtilsSpec to validate partitioning behavior and Java→Scala map conversion.
• Add DistributedAggregationSpec to pin the case-class contract and a worked end-to-end average aggregation.
• Add URLFetchUtilSpec to cover success/failure paths and retry semantics for URL input streams.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
common/workflow-operator/src/test/scala/org/apache/texera/amber/operator/util/OperatorDescriptorUtilsSpec.scala	New spec for equallyPartitionGoal and toImmutableMap behavior.
common/workflow-operator/src/test/scala/org/apache/texera/amber/operator/aggregate/DistributedAggregationSpec.scala	New spec covering DistributedAggregation function members and average example.
common/workflow-operator/src/test/scala/org/apache/texera/amber/operator/source/fetcher/URLFetchUtilSpec.scala	New spec for URLFetchUtil.getInputStreamFromURL success/failure and retries.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[github-actions]

⚠️ Benchmark changes need a look

🟢 2 better · 🔴 3 worse · ⚪ 10 noise (<±5%) · 0 without baseline

Compared against main d513324 benchmarked on this same runner, so the delta is largely free of cross-runner hardware noise. The "7d avg" column still reflects the gh-pages dashboard. Treat <±5% as noise unless repeated.

Dashboard · Run

	config	throughput	MB/s	latency	max Δ latest / 7d
🔴	bs=10 sw=10 sl=64	397	0.242	24,436/35,183/35,183 us	🟢 -25.5% / ⚪ within ±5%
🔴	bs=100 sw=10 sl=64	830	0.506	116,595/154,145/154,145 us	🔴 +9.1% / 🔴 +10.3%
⚪	bs=1000 sw=10 sl=64	948	0.578	1,058,901/1,093,153/1,093,153 us	⚪ within ±5% / 🔴 -9.0%

Baseline details

Latest main d513324 from same runner

config	metric	PR	latest main	7d avg	Δ latest	Δ 7d
bs=10 sw=10 sl=64	throughput	397 tuples/sec	400 tuples/sec	410.82 tuples/sec	-0.8%	-3.4%
bs=10 sw=10 sl=64	MB/s	0.242 MB/s	0.244 MB/s	0.251 MB/s	-0.8%	-3.5%
bs=10 sw=10 sl=64	p50	24,436 us	21,538 us	23,785 us	+13.5%	+2.7%
bs=10 sw=10 sl=64	p95	35,183 us	47,232 us	34,980 us	-25.5%	+0.6%
bs=10 sw=10 sl=64	p99	35,183 us	47,232 us	34,980 us	-25.5%	+0.6%
bs=100 sw=10 sl=64	throughput	830 tuples/sec	867 tuples/sec	891.94 tuples/sec	-4.3%	-6.9%
bs=100 sw=10 sl=64	MB/s	0.506 MB/s	0.529 MB/s	0.544 MB/s	-4.3%	-7.1%
bs=100 sw=10 sl=64	p50	116,595 us	112,907 us	112,277 us	+3.3%	+3.8%
bs=100 sw=10 sl=64	p95	154,145 us	141,286 us	139,802 us	+9.1%	+10.3%
bs=100 sw=10 sl=64	p99	154,145 us	141,286 us	139,802 us	+9.1%	+10.3%
bs=1000 sw=10 sl=64	throughput	948 tuples/sec	959 tuples/sec	1,041 tuples/sec	-1.1%	-8.9%
bs=1000 sw=10 sl=64	MB/s	0.578 MB/s	0.585 MB/s	0.635 MB/s	-1.2%	-9.0%
bs=1000 sw=10 sl=64	p50	1,058,901 us	1,046,928 us	972,714 us	+1.1%	+8.9%
bs=1000 sw=10 sl=64	p95	1,093,153 us	1,074,763 us	1,023,057 us	+1.7%	+6.9%
bs=1000 sw=10 sl=64	p99	1,093,153 us	1,074,763 us	1,023,057 us	+1.7%	+6.9%

Raw CSV

config_idx,batch_size,schema_width,string_len,num_batches,total_ms,total_tuples,total_bytes,tuples_per_sec,mb_per_sec,lat_p50_us,lat_p95_us,lat_p99_us
0,10,10,64,20,503.44,200,128000,397,0.242,24435.54,35182.71,35182.71
1,100,10,64,20,2410.62,2000,1280000,830,0.506,116595.48,154144.63,154144.63
2,1000,10,64,20,21107.21,20000,12800000,948,0.578,1058901.08,1093153.41,1093153.41

[xuang7]

LGTM!