java-topology/defects/erpnext-0001/test/test_erpnext_0001.java

import java.util.*;

/**
 * Unit test for erpnext-0001: BOM.get_children() list dedup O(B^2)
 *
 * Simulates the BOM explosion BFS traversal where child_bom membership
 * is checked via list scan (defect) vs set lookup (fix).
 *
 * Defect: bom.py lines 924-931 — "if child_bom not in bom_list" where
 * bom_list is a Python list, giving O(B) per check and O(B^2) overall.
 *
 * Fix: maintain a parallel set for O(1) membership checks.
 */
public class test_erpnext_0001 {

    // --- Defect: list-only BFS dedup ---
    static List<String> getBomChildrenDefect(Map<String, List<String>> bomTree, String root) {
        List<String> bomList = new ArrayList<>();
        bomList.add(root);
        int count = 0;
        while (count < bomList.size()) {
            List<String> children = bomTree.getOrDefault(bomList.get(count), Collections.emptyList());
            for (String child : children) {
                if (!bomList.contains(child)) {  // O(N) per check
                    bomList.add(child);
                }
            }
            count++;
        }
        Collections.reverse(bomList);
        return bomList;
    }

    // --- Fix: set-backed BFS dedup ---
    static List<String> getBomChildrenFixed(Map<String, List<String>> bomTree, String root) {
        List<String> bomList = new ArrayList<>();
        Set<String> bomSet = new HashSet<>();
        bomList.add(root);
        bomSet.add(root);
        int count = 0;
        while (count < bomList.size()) {
            List<String> children = bomTree.getOrDefault(bomList.get(count), Collections.emptyList());
            for (String child : children) {
                if (!bomSet.contains(child)) {  // O(1) per check
                    bomList.add(child);
                    bomSet.add(child);
                }
            }
            count++;
        }
        Collections.reverse(bomList);
        return bomList;
    }

    // Build a BOM tree with N levels, each having fanout children
    static Map<String, List<String>> buildBomTree(int levels, int fanout) {
        Map<String, List<String>> tree = new HashMap<>();
        int id = 0;
        Queue<String> queue = new LinkedList<>();
        String root = "BOM-" + (id++);
        queue.add(root);

        for (int level = 0; level < levels && !queue.isEmpty(); level++) {
            int size = queue.size();
            for (int i = 0; i < size; i++) {
                String parent = queue.poll();
                List<String> children = new ArrayList<>();
                for (int j = 0; j < fanout; j++) {
                    String child = "BOM-" + (id++);
                    children.add(child);
                    queue.add(child);
                }
                tree.put(parent, children);
            }
        }
        return tree;
    }

    public static void main(String[] args) {
        System.out.println("=== erpnext-0001: BOM get_children list dedup O(B^2) ===\n");

        // Correctness test
        Map<String, List<String>> smallTree = new HashMap<>();
        smallTree.put("BOM-ROOT", Arrays.asList("BOM-A", "BOM-B"));
        smallTree.put("BOM-A", Arrays.asList("BOM-C", "BOM-B"));  // BOM-B appears twice
        smallTree.put("BOM-B", Arrays.asList("BOM-D"));
        smallTree.put("BOM-C", Collections.emptyList());
        smallTree.put("BOM-D", Collections.emptyList());

        List<String> defectResult = getBomChildrenDefect(smallTree, "BOM-ROOT");
        List<String> fixedResult = getBomChildrenFixed(smallTree, "BOM-ROOT");

        assert defectResult.equals(fixedResult) :
            "Results differ: defect=" + defectResult + " fixed=" + fixedResult;
        System.out.println("Correctness: PASS (both produce " + fixedResult + ")");

        // Performance test: BOM tree with 500 unique BOMs
        int levels = 5, fanout = 3;
        Map<String, List<String>> bigTree = buildBomTree(levels, fanout);
        String root = "BOM-0";
        int totalBoms = bigTree.values().stream().mapToInt(List::size).sum() + 1;
        System.out.println("BOM tree: " + totalBoms + " nodes, " + levels + " levels, fanout=" + fanout);

        // Warmup
        for (int i = 0; i < 5; i++) {
            getBomChildrenDefect(bigTree, root);
            getBomChildrenFixed(bigTree, root);
        }

        int iterations = 500;
        long t0 = System.nanoTime();
        for (int i = 0; i < iterations; i++) {
            getBomChildrenDefect(bigTree, root);
        }
        long defectNs = System.nanoTime() - t0;

        t0 = System.nanoTime();
        for (int i = 0; i < iterations; i++) {
            getBomChildrenFixed(bigTree, root);
        }
        long fixedNs = System.nanoTime() - t0;

        double ratio = (double) defectNs / fixedNs;
        System.out.printf("Defect: %,d ns / %d iters%n", defectNs, iterations);
        System.out.printf("Fixed:  %,d ns / %d iters%n", fixedNs, iterations);
        System.out.printf("Ratio:  %.1fx%n", ratio);

        boolean pass = ratio > 1.5;
        System.out.println("\nResult: " + (pass ? "PASS" : "FAIL") + " (ratio=" + String.format("%.1f", ratio) + "x)");
        assert pass : "Expected speedup > 1.5x, got " + ratio;
    }
}