test(workflow-execution-service): extend ResultExportService unit test coverage

[mengw15]

What changes were proposed in this PR?

ResultExportService sits at ~6% line coverage: the existing spec only covers parseOperators and validateExportRequest, leaving the whole export-encoding layer untested. The streamDocumentAs* writers look storage-bound but are not — each takes a VirtualDocument[Tuple] parameter, so a small in-spec fake document makes them testable against a ByteArrayOutputStream, with no Iceberg, MinIO or DB.

This extends ResultExportServiceSpec with 19 tests that reach the private writers through PrivateMethodTester: streamDocumentAsCSV (both early returns, inferred vs supplied headers, and a document larger than Constants.CHUNK_SIZE to exercise the buffered chunk loop), streamCellData (rowIndex/columnIndex validation messages, an unretrievable row, and the happy-path bytes), convertFieldToBytes (all three branches), streamDocumentAsHTML, streamDocumentAsParquetZip (verbatim copy plus source-stream close, and error propagation), streamDocumentAsArrow (round-trips the tuples back through ArrowFileReader), and NonClosingOutputStream.

Two existing behaviors are pinned as-is rather than changed: with supplied headers the first row is not consumed by header inference, so it still appears in the body (the asymmetry against the None branch), and streamDocumentAsHTML throws NoSuchElementException on an empty document because .head is unguarded. getOperatorDocument, saveToDatasets, saveStreamToDataset and generateFileName stay uncovered — they need DocumentFactory.openDocument, a live file-service endpoint, or embed LocalDateTime.now().

Any related issues, documentation, discussions?

Closes #6898. Extends the spec added by #6705.

How was this PR tested?

sbt "WorkflowExecutionService/testOnly *ResultExportServiceSpec" passes with 24 tests (5 existing, 19 new); Test/scalafmtCheck and Test/scalafix --check are clean. Verified the failure path by inverting the supplied-headers assertion and confirming the suite went red and exited non-zero. Every test runs in-process against an in-spec fake document, so no external service is involved.

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

Generated-by: Claude Code (Fable 5)

[github-actions]

Automated Reviewer Suggestions

Based on the git blame history of the changed files, we recommend the following reviewers:

• Contributors with relevant context: @Ma77Ball
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[Copilot]

Pull request overview

Expands unit test coverage for ResultExportService’s export/encoding writer methods (CSV, Arrow, HTML, Parquet zip, single-cell data) by invoking private helpers via ScalaTest’s PrivateMethodTester and using an in-memory VirtualDocument fake to avoid external storage dependencies.

Changes:

• Adds an in-spec VirtualDocument[Tuple] fake plus tracking input/output streams to test writer behavior in-process.
• Introduces new tests covering CSV header behaviors, chunked CSV streaming, cell extraction/validation, field-to-bytes conversion, HTML export, Parquet-zip copy/close semantics, Arrow round-trip, and NonClosingOutputStream.

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[github-actions]

⚠️ Benchmark changes need a look

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

Compared against main 4af3a85 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	365	0.223	26,467/36,419/36,419 us	🔴 +8.7% / 🔴 +119.5%
⚪	bs=100 sw=10 sl=64	795	0.485	125,728/151,800/151,800 us	⚪ within ±5% / 🔴 +39.1%
⚪	bs=1000 sw=10 sl=64	896	0.547	1,122,018/1,142,495/1,142,495 us	⚪ within ±5% / 🔴 +11.9%

Baseline details

Latest main 4af3a85 from same runner

config	metric	PR	latest main	7d avg	Δ latest	Δ 7d
bs=10 sw=10 sl=64	throughput	365 tuples/sec	397 tuples/sec	754.55 tuples/sec	-8.1%	-51.6%
bs=10 sw=10 sl=64	MB/s	0.223 MB/s	0.242 MB/s	0.461 MB/s	-7.9%	-51.6%
bs=10 sw=10 sl=64	p50	26,467 us	24,479 us	12,816 us	+8.1%	+106.5%
bs=10 sw=10 sl=64	p95	36,419 us	33,500 us	16,594 us	+8.7%	+119.5%
bs=10 sw=10 sl=64	p99	36,419 us	33,500 us	19,806 us	+8.7%	+83.9%
bs=100 sw=10 sl=64	throughput	795 tuples/sec	823 tuples/sec	969.38 tuples/sec	-3.4%	-18.0%
bs=100 sw=10 sl=64	MB/s	0.485 MB/s	0.502 MB/s	0.592 MB/s	-3.4%	-18.0%
bs=100 sw=10 sl=64	p50	125,728 us	119,975 us	103,584 us	+4.8%	+21.4%
bs=100 sw=10 sl=64	p95	151,800 us	150,180 us	109,097 us	+1.1%	+39.1%
bs=100 sw=10 sl=64	p99	151,800 us	150,180 us	117,304 us	+1.1%	+29.4%
bs=1000 sw=10 sl=64	throughput	896 tuples/sec	911 tuples/sec	1,004 tuples/sec	-1.6%	-10.7%
bs=1000 sw=10 sl=64	MB/s	0.547 MB/s	0.556 MB/s	0.613 MB/s	-1.6%	-10.7%
bs=1000 sw=10 sl=64	p50	1,122,018 us	1,097,333 us	1,002,357 us	+2.2%	+11.9%
bs=1000 sw=10 sl=64	p95	1,142,495 us	1,151,730 us	1,046,463 us	-0.8%	+9.2%
bs=1000 sw=10 sl=64	p99	1,142,495 us	1,151,730 us	1,073,661 us	-0.8%	+6.4%

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
0,10,10,64,20,547.88,200,128000,365,0.223,26466.77,36418.75,36418.75
1,100,10,64,20,2517.26,2000,1280000,795,0.485,125728.42,151799.70,151799.70
2,1000,10,64,20,22323.78,20000,12800000,896,0.547,1122017.85,1142494.95,1142494.95

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.52%. Comparing base (4af3a85) to head (18adb51).

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #6902      +/-   ##
============================================
+ Coverage     78.39%   78.52%   +0.13%     
- Complexity     3723     3750      +27     
============================================
  Files          1161     1161              
  Lines         46066    46066              
  Branches       5107     5107              
============================================
+ Hits          36112    36173      +61     
+ Misses         8343     8281      -62     
- Partials       1611     1612       +1     

Flag	Coverage Δ		*Carryforward flag
access-control-service	70.00% <ø> (ø)		Carriedforward from 4af3a85
agent-service	76.76% <ø> (ø)		Carriedforward from 4af3a85
amber	71.87% <ø> (+0.36%)	⬆️
computing-unit-managing-service	20.49% <ø> (ø)		Carriedforward from 4af3a85
config-service	66.66% <ø> (ø)		Carriedforward from 4af3a85
file-service	67.21% <ø> (ø)		Carriedforward from 4af3a85
frontend	82.64% <ø> (ø)		Carriedforward from 4af3a85
notebook-migration-service	78.94% <ø> (ø)		Carriedforward from 4af3a85
pyamber	93.48% <ø> (ø)		Carriedforward from 4af3a85
workflow-compiling-service	55.14% <ø> (ø)		Carriedforward from 4af3a85

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

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[aglinxinyuan]

LGTM!