Extend TestSchedulingUtils with top level union

[losipiuk]

Add some missing test coverage

Summary by Sourcery

Tests:

• Add test for canStream over a union operator with multiple child sources

[sourcery-ai]

Reviewer's Guide

Add missing test coverage for top-level UNION in SchedulingUtils by implementing a new test method that verifies canStream behavior for each branch of a UNION stage.

File-Level Changes

Change	Details	Files
Introduce testCanStreamUnion to verify streaming through a UNION operator.	Define separate SubPlans and RemoteSourceNodes for branches a, b, c Construct a parent SubPlan with a UNION node referencing the branch sources Assert that SchedulingUtils.canStream returns true for each branch	core/trino-main/src/test/java/io/trino/execution/scheduler/TestSchedulingUtils.java

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[sourcery-ai]

Hey there - I've reviewed your changes - here's some feedback:

• In testCanStreamUnion you forgot to include cSubPlan in the createSubPlan children list, so you should pass ImmutableList.of(aSubPlan, bSubPlan, cSubPlan) instead of just a and b.
• Consider adding a negative test where one union child cannot stream so you assert that canStream(parent, child) returns false when any branch is non‐streamable.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- In testCanStreamUnion you forgot to include cSubPlan in the createSubPlan children list, so you should pass ImmutableList.of(aSubPlan, bSubPlan, cSubPlan) instead of just a and b.
- Consider adding a negative test where one union child cannot stream so you assert that canStream(parent, child) returns false when any branch is non‐streamable.

## Individual Comments

### Comment 1
<location> `core/trino-main/src/test/java/io/trino/execution/scheduler/TestSchedulingUtils.java:93-96` </location>
<code_context>
+        SubPlan cSubPlan = valuesSubPlan("c");
+        RemoteSourceNode remoteSourceC = remoteSource("c");
+
+        SubPlan parentSubPlan = createSubPlan(
+                "parent",
+                union("union", ImmutableList.of(remoteSourceA, remoteSourceB, remoteSourceC)),
+                ImmutableList.of(aSubPlan, bSubPlan));
+
+        assertThat(SchedulingUtils.canStream(parentSubPlan, aSubPlan)).isTrue();
</code_context>

<issue_to_address>
**question (testing):** Check if all union children are included in parentSubPlan's children.

Please verify that cSubPlan is either intentionally excluded or properly accounted for; otherwise, the test may not represent the union's full structure.
</issue_to_address>

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[sourcery-ai]

question (testing): Check if all union children are included in parentSubPlan's children.

Please verify that cSubPlan is either intentionally excluded or properly accounted for; otherwise, the test may not represent the union's full structure.

[chenjian2664]

Why cSubPlan isn't a child of "parent"?