[incubator-kie-issues#2181] make KOptListMoveIteratorTest deterministic using LinkedHashMap

[hwu2024]

Issue

• Fixes Non-deterministic order in KOptListMoveIteratorTest due to HashMap iteration incubator-kie-issues#2181

Fixes

We make the test deterministic by using a LinkedHashMap for entityToListSize, so the iteration order is the encounter order of entities

Map<Object, Integer> entityToListSize = Arrays.stream(entities)
        .collect(Collectors.toMap(
                Function.identity(),
                entity -> 2,
                Integer::sum,
                LinkedHashMap::new));

This preserves the expected ordering while keeping the rest of the test logic.

JIRA

Referenced pull requests

Checklist

• Documentation updated if applicable.
• Release notes updated if applicable.
• Upgrade recipe provided if applicable.

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[Rikkola]

Hi @hwu2024 is it possible to make an unit test that proves the bug?

[hwu2024]

Hi @Rikkola thanks for the review!

The core problem is that setupValidNonsequential4OptMove used Collectors.toMap() with the default HashMap, and then iterated entityToListSize.entrySet(). That makes the per‑entity lists depend on the HashMap iteration order, which HashMap makes no guarantees as to the order of the map. NonDex exposes this by shuffling that iterator and we can also trace the error by running the debug mode:

mvn -pl core/optaplanner-core-impl edu.illinois:nondex-maven-plugin:2.2.1:debug -Dtest=org.optaplanner.core.impl.heuristic.selector.move.generic.list.kopt.KOptListMoveIteratorTest#testNonsequentialKOptOnDifferentEntity

which the debug stack shows that

java.util.HashMap$EntrySet.iterator(HashMap.java:1106)
org.optaplanner.core.impl.heuristic.selector.move.generic.list.kopt.KOptListMoveIteratorTest.setupValidNonsequential4OptMove(KOptListMoveIteratorTest.java:233)

We can also reproduce by manually building two maps with the same keys/values but different iteration order (simulating HashMap), and runs the same list‑building logic as setupValidNonsequential4OptMove.

@Test
void entityToListDependsOnMapIterationOrder() {
    int k = 4;
    Object[] data = new Object[2 * k + 8];
    for (int i = 0; i < data.length; i++) {
        data[i] = "v" + i;
    }

    Map<Object, Integer> entityToListSizeOrder1 = new LinkedHashMap<>();
    entityToListSizeOrder1.put("e1", 6);
    entityToListSizeOrder1.put("e2", 4);

    Map<Object, Integer> entityToListSizeOrder2 = new LinkedHashMap<>();
    entityToListSizeOrder2.put("e2", 4);
    entityToListSizeOrder2.put("e1", 6);

    Map<Object, List<Object>> entityToList1 =
            buildEntityToListLikeNonsequentialHelper(entityToListSizeOrder1, data);
    Map<Object, List<Object>> entityToList2 =
            buildEntityToListLikeNonsequentialHelper(entityToListSizeOrder2, data);

    assertThat(entityToList1).isEqualTo(entityToList2);
}

private static Map<Object, List<Object>> buildEntityToListLikeNonsequentialHelper(
        Map<Object, Integer> entityToListSize, Object[] data) {
    Map<Object, List<Object>> entityToList = new HashMap<>();
    int offset = 0;
    for (Map.Entry<Object, Integer> entry : entityToListSize.entrySet()) {
        Object entity = entry.getKey();
        int listSize = entry.getValue();
        List<Object> entityList = new ArrayList<>(Arrays.asList(data).subList(offset, offset + listSize));
        for (int i = 0; i < listSize; i++) {
            entityList.add(2 * i + 1, entity + "-extra-" + i);
        }
        entityList.add(0, entity + "-start");
        entityList.add(entity + "-end");
        entityToList.put(entity, entityList);
        offset += listSize;
    }
    return entityToList;
}

and if we run

mvn -pl core/optaplanner-core-impl test -Dtest=org.optaplanner.core.impl.heuristic.selector.move.generic.list.kopt.KOptListMoveIteratorTest#entityToListDependsOnMapIterationOrder

we get

expected: 
  {"e1"=["e1-start",
      "v4",
      "e1-extra-0",
      "v5",
      "e1-extra-1",
      "v6",
      "e1-extra-2",
      "v7",
      "e1-extra-3",
      "v8",
      "e1-extra-4",
      "v9",
      "e1-extra-5",
      "e1-end"], "e2"=["e2-start",
      "v0",
      "e2-extra-0",
      "v1",
      "e2-extra-1",
      "v2",
      "e2-extra-2",
      "v3",
      "e2-extra-3",
      "e2-end"]}
 but was: 
  {"e1"=["e1-start",
      "v0",
      "e1-extra-0",
      "v1",
      "e1-extra-1",
      "v2",
      "e1-extra-2",
      "v3",
      "e1-extra-3",
      "v4",
      "e1-extra-4",
      "v5",
      "e1-extra-5",
      "e1-end"], "e2"=["e2-start",
      "v6",
      "e2-extra-0",
      "v7",
      "e2-extra-1",
      "v8",
      "e2-extra-2",
      "v9",
      "e2-extra-3",
      "e2-end"]}

It shows that the old logic using default HashMap was order‑sensitive. The LinkedHashMap change in this PR then removes that bug.

Thanks again for your time to follow up!

[Copilot]

Pull request overview

This PR addresses non-deterministic test failures in KOptListMoveIteratorTest by ensuring predictable iteration order when processing entities. The fix uses LinkedHashMap instead of the default HashMap to preserve insertion order.

Key changes:

• Added LinkedHashMap import
• Modified Collectors.toMap call in setupValidNonsequential4OptMove to use LinkedHashMap::new as the map supplier

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[Copilot]

This fix is incomplete. The same non-deterministic issue exists in the setupValidOddSequentialKOptMove method at lines 134-137, where entityToListSize is also created using Collectors.toMap without specifying LinkedHashMap::new as the map supplier. Both methods iterate over entityToListSize.entrySet() (line 142 in setupValidOddSequentialKOptMove, line 235 in this method) and rely on the iteration order matching the entities array order for correctness. The setupValidOddSequentialKOptMove method should receive the same fix to ensure full test determinism.