java-topology/defects/hive/unit/TestTaskTrackerVisited.java

import java.util.*;

/**
 * Unit test for hive-0001: TaskTracker.updateTaskCount ArrayList visited O(T²)
 *
 * Simulates the defective and fixed versions side by side.
 * The fix: change ArrayList to HashSet for the visited accumulator.
 */
public class TestTaskTrackerVisited {

    // --- Simulate defective version (ArrayList visited) ---

    static int countOpsDefective;

    static void updateTaskCountDefective(MockTask task, List<MockTask> visited) {
        visited.add(task);
        for (MockTask child : task.children) {
            countOpsDefective++;                     // count the contains() check
            if (visited.contains(child)) {           // O(T) linear scan
                continue;
            }
            updateTaskCountDefective(child, visited);
        }
    }

    static int runDefective(MockTask root) {
        countOpsDefective = 0;
        List<MockTask> visited = new ArrayList<>();
        updateTaskCountDefective(root, visited);
        return countOpsDefective;
    }

    // --- Simulate fixed version (HashSet visited) ---

    static int countOpsFixed;

    static void updateTaskCountFixed(MockTask task, Set<MockTask> visited) {
        visited.add(task);
        for (MockTask child : task.children) {
            countOpsFixed++;                         // count the contains() check
            if (visited.contains(child)) {           // O(1) hash lookup
                continue;
            }
            updateTaskCountFixed(child, visited);
        }
    }

    static int runFixed(MockTask root) {
        countOpsFixed = 0;
        Set<MockTask> visited = new HashSet<>();
        updateTaskCountFixed(root, visited);
        return countOpsFixed;
    }

    // --- MockTask for test ---

    static class MockTask {
        final String name;
        final List<MockTask> children = new ArrayList<>();

        MockTask(String name) { this.name = name; }

        void addChild(MockTask child) { children.add(child); }

        @Override
        public int hashCode() { return name.hashCode(); }

        @Override
        public boolean equals(Object o) {
            return o instanceof MockTask && ((MockTask) o).name.equals(name);
        }
    }

    // Build a diamond DAG: root -> [A, B, C, ...] -> shared_sink
    static MockTask buildDiamondDAG(int branches) {
        MockTask root = new MockTask("root");
        MockTask sink = new MockTask("sink");
        for (int i = 0; i < branches; i++) {
            MockTask branch = new MockTask("branch-" + i);
            branch.addChild(sink);
            root.addChild(branch);
        }
        return root;
    }

    // Build a chain: t0 -> t1 -> ... -> tN
    static MockTask buildChain(int n) {
        MockTask[] tasks = new MockTask[n];
        for (int i = 0; i < n; i++) {
            tasks[i] = new MockTask("task-" + i);
        }
        for (int i = 0; i < n - 1; i++) {
            tasks[i].addChild(tasks[i + 1]);
        }
        return tasks[0];
    }

    public static void main(String[] args) {
        int pass = 0, fail = 0;

        // Test 1: chain of 50 tasks — both should produce same traversal count
        {
            MockTask root = buildChain(50);
            int defOps = runDefective(root);
            int fixOps = runFixed(root);
            boolean ok = (defOps == fixOps);  // chain: no revisits, same count
            System.out.printf("[%s] Chain-50: defective=%d ops, fixed=%d ops%n",
                ok ? "PASS" : "FAIL", defOps, fixOps);
            if (ok) pass++; else fail++;
        }

        // Test 2: diamond DAG with 10 branches — defective pays O(T) per revisit check
        {
            MockTask root = buildDiamondDAG(10);
            int defOps = runDefective(root);
            int fixOps = runFixed(root);
            // Fixed ops == defective ops here (both iterate same children)
            // The difference is the *cost* of contains() - we verify both count same checks
            boolean ok = (defOps == fixOps);
            System.out.printf("[%s] Diamond-10: defective=%d ops, fixed=%d ops%n",
                ok ? "PASS" : "FAIL", defOps, fixOps);
            if (ok) pass++; else fail++;
        }

        // Test 3: large diamond DAG — measure relative op counts are equal
        {
            MockTask root = buildDiamondDAG(100);
            int defOps = runDefective(root);
            int fixOps = runFixed(root);
            boolean ok = (defOps == fixOps);
            System.out.printf("[%s] Diamond-100: defective=%d ops, fixed=%d ops%n",
                ok ? "PASS" : "FAIL", defOps, fixOps);
            if (ok) pass++; else fail++;
        }

        // Test 4: correctness — both versions visit same number of unique nodes
        {
            MockTask root = buildDiamondDAG(20);
            // Count unique nodes in defective traversal
            List<MockTask> visitedDef = new ArrayList<>();
            countOpsDefective = 0;
            updateTaskCountDefective(root, visitedDef);
            int uniqueDef = new HashSet<>(visitedDef).size();

            Set<MockTask> visitedFix = new HashSet<>();
            countOpsFixed = 0;
            updateTaskCountFixed(root, visitedFix);
            int uniqueFix = visitedFix.size();

            boolean ok = (uniqueDef == uniqueFix);
            System.out.printf("[%s] Correctness Diamond-20: defective=%d unique, fixed=%d unique%n",
                ok ? "PASS" : "FAIL", uniqueDef, uniqueFix);
            if (ok) pass++; else fail++;
        }

        // Test 5: performance ratio — defective contains() is O(N) vs O(1) for fixed
        // We simulate by counting the cost of each contains() call
        {
            int N = 200;
            MockTask root = buildDiamondDAG(N);
            // Defective: every contains() call scans the whole list - cost = list.size() at call time
            int[] defCost = {0};
            simulateDefectiveCost(root, new ArrayList<>(), defCost);
            // Fixed: every contains() is O(1) - cost = 1
            int[] fixCost = {0};
            simulateFixedCost(root, new HashSet<>(), fixCost);

            double ratio = (double) defCost[0] / fixCost[0];
            boolean ok = ratio >= 50.0;  // expect significant speedup at N=200
            System.out.printf("[%s] Cost ratio Diamond-%d: defective=%d, fixed=%d, ratio=%.1fx%n",
                ok ? "PASS" : "FAIL", N, defCost[0], fixCost[0], ratio);
            if (ok) pass++; else fail++;
        }

        System.out.printf("%nResult: %d PASS, %d FAIL%n", pass, fail);
        System.exit(fail > 0 ? 1 : 0);
    }

    static void simulateDefectiveCost(MockTask task, List<MockTask> visited, int[] cost) {
        visited.add(task);
        for (MockTask child : task.children) {
            cost[0] += visited.size();  // O(N) for ArrayList.contains
            if (visited.contains(child)) continue;
            simulateDefectiveCost(child, visited, cost);
        }
    }

    static void simulateFixedCost(MockTask task, Set<MockTask> visited, int[] cost) {
        visited.add(task);
        for (MockTask child : task.children) {
            cost[0] += 1;              // O(1) for HashSet.contains
            if (visited.contains(child)) continue;
            simulateFixedCost(child, visited, cost);
        }
    }
}