test: Add end to end tests for quantile digest functions

[allenshen13]

Description

Add end-to-end tests for the quantile digest (qdigest) functions on the native worker: qdigest_agg (all
three variants), merge, value_at_quantile, values_at_quantiles, and scale_qdigest.

Motivation and Context

Closes #26939. The qdigest functions are registered in Velox
but had no e2e coverage comparing Java vs native worker results.

Impact

Tests only. No user-facing or API changes.

Test Plan

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Release Notes

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Summary by Sourcery

Add end-to-end native worker coverage for qdigest aggregation and related functions to ensure consistency with Java execution.

Tests:

• Add native worker tests covering qdigest_agg for bigint, double, and real inputs, including weighted and accuracy-parameter variants.
• Add tests for qdigest merge, value_at_quantile, values_at_quantiles, and scale_qdigest behavior on the nation dataset, including null-handling cases.

[sourcery-ai]

Reviewer's Guide

Adds an end-to-end native worker aggregation test covering all qdigest functions (aggregation variants, merge, value_at_quantile, values_at_quantiles, and scale_qdigest) to ensure parity with Java execution.

File-Level Changes

Change	Details	Files
Add a consolidated end-to-end test for qdigest aggregation and related functions in the native worker aggregation test suite.	Introduce testQDigestFunctions() to AbstractTestNativeAggregations to validate qdigest_agg over bigint, double, and real inputs Add assertions for weighted and accuracy-parameterized qdigest_agg variants using value_at_quantile Test merge of per-group qdigests and validate results via value_at_quantile and values_at_quantiles Verify scale_qdigest behavior by scaling a qdigest and checking the quantile result Cover null-handling behavior for qdigest_agg, including all-null input	presto-native-execution/src/test/java/com/facebook/presto/nativeworker/AbstractTestNativeAggregations.java

Assessment against linked issues

Issue	Objective	Addressed	Explanation
#26939	Add end-to-end tests for the scale_qdigest quantile digest function.	✅
#26939	Add end-to-end tests for other quantile digest functions that were missing coverage (e.g., qdigest_agg variants, merge, value_at_quantile, values_at_quantiles).	✅

Possibly linked issues

• Add end to end tests for quantile digest functions #26939: PR implements the requested end-to-end tests for qdigest functions, including scale_qdigest, fulfilling the issue.

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[sourcery-ai]

Hey - I've found 1 issue

Prompt for AI Agents

Please address the comments from this code review:

## Individual Comments

### Comment 1
<location path="presto-native-execution/src/test/java/com/facebook/presto/nativeworker/AbstractTestNativeAggregations.java" line_range="361" />
<code_context>
+    public void testQDigestFunctions()
+    {
+        // bigint, double, real
+        assertQuery("SELECT value_at_quantile(qdigest_agg(nationkey), 0e0) FROM nation", "SELECT BIGINT '0'");
+        assertQuery("SELECT value_at_quantile(qdigest_agg(cast(nationkey as DOUBLE)), 0e0) FROM nation", "SELECT DOUBLE '0'");
+        assertQuery("SELECT value_at_quantile(qdigest_agg(cast(nationkey as REAL)), 0e0) FROM nation", "SELECT REAL '0'");
</code_context>
<issue_to_address>
**suggestion (testing):** Add coverage for non-endpoint quantiles (e.g. 0.5) to better validate qdigest accuracy semantics.

Current assertions only cover endpoint quantiles (0 or 1), where behavior is less interesting for an approximate structure like qdigest. Please add at least one assertion for an interior quantile (e.g., 0.25, 0.5, 0.9) on a non-trivial distribution to better exercise the core quantile calculation and native vs Java consistency.
</issue_to_address>

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[sourcery-ai]

suggestion (testing): Add coverage for non-endpoint quantiles (e.g. 0.5) to better validate qdigest accuracy semantics.

Current assertions only cover endpoint quantiles (0 or 1), where behavior is less interesting for an approximate structure like qdigest. Please add at least one assertion for an interior quantile (e.g., 0.25, 0.5, 0.9) on a non-trivial distribution to better exercise the core quantile calculation and native vs Java consistency.

[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

Scanned Files

None

[pramodsatya]

Thanks for adding these tests @allenshen13. Could you please move these to AbstractTestAggregationsNative in presto-native-tests so it has expanded test coverage? Some of these function tests are already covered there as well.