KAFKA-19429: Deflake streams_smoke_test

[lucasbru]

It looks like we are checking for properties that are not guaranteed
under at_least_once, for example, exact counting (not allowing for
overcounting).

This change relaxes the validation constraint to only check that we
counted at least N messages, and our sums come out as at least the
expected sum.

Reviewers: Matthias J. Sax matthias@confluent.io

[lucasbru]

PTAL @aliehsaeedii

[Copilot]

Pull Request Overview

Relax the smoke test validation to only require at least the expected counts and sums under at-least-once semantics (non-EOS), while preserving exact validation for EOS.

• Introduce a validationPredicate to switch between exact (equals) and at-least (>=) checks
• Refactor all verify and verifyTAgg calls to accept the new predicate
• Add lessEquals helper for the at-least-once comparison logic

Comments suppressed due to low confidence (3)

streams/src/test/java/org/apache/kafka/streams/tests/SmokeTestDriver.java:517

• [nitpick] Consider renaming validationPredicate to something like comparisonPredicate or valueComparator to clarify that it encapsulates the comparison operation between expected and actual values.

        final BiPredicate<Number, Number> validationPredicate;

streams/src/test/java/org/apache/kafka/streams/tests/SmokeTestDriver.java:665

• Add unit tests for the new at-least-once (lessEquals) predicate and the EOS vs non-EOS validation paths in both verifyTAgg and verify to ensure the new logic behaves as expected.

                                      final BiPredicate<Number, Number> validationPredicate,

[lucasbru]

Test run results https://confluent-open-source-kafka-branch-builder-system-test-results.s3-us-west-2.amazonaws.com/trunk/2025-06-23--001.02295be1-b01d-4ad9-b36d-6b9d0a06bbf5--1750694196--lucasbru--deflake_streams_smoke_test--c9717bf50d/report.html