java-topology/tests/unit/Moad0005UnitTest.java

package unit;

import support.Moad0005Algorithm;
import support.Moad0005Algorithm.DefectiveCache;
import support.Moad0005Algorithm.FixedCache;

/**
 * Unit tests for MOAD-0005: CWE-362 — A Thundering Herd.
 *
 * Proves from first principles:
 *   1. Defective: N callers all seeing a null cache entry all invoke
 *      expensiveCompute() — N computes instead of 1.  This is the herd.
 *   2. Fixed: ConcurrentHashMap.computeIfAbsent() ensures exactly 1 compute
 *      regardless of how many callers miss simultaneously.
 *   3. Both return the same (correct) value for any key.
 *   4. Sequential access on a warm cache: both call compute exactly once.
 *
 * The single-threaded simulation models the race window: all callers read
 * before any caller's put() completes.  Integration tests use real threads.
 *
 * No build tool required. Compile and run:
 *
 *   cd tests
 *   java -m jdk.compiler/com.sun.tools.javac.Main -cp . \
 *        support/Moad0005Algorithm.java unit/Moad0005UnitTest.java
 *   java -cp . unit.Moad0005UnitTest
 */
public class Moad0005UnitTest {

    private static int passed = 0;
    private static int failed = 0;

    public static void main(String[] args) {
        System.out.println("=== Moad0005UnitTest (A Thundering Herd) ===\n");

        System.out.println("-- Correctness: both caches return correct value --");
        testDefectiveReturnsCorrectValue();
        testFixedReturnsCorrectValue();
        testBothReturnSameValue();

        System.out.println("\n-- Defect: N concurrent misses produce N computes --");
        testDefectiveConcurrentMissN10();
        testDefectiveConcurrentMissN50();
        testDefectiveComputeCountScalesWithCallers();

        System.out.println("\n-- Fix: N concurrent misses produce exactly 1 compute --");
        testFixedConcurrentMissN10();
        testFixedConcurrentMissN50();
        testFixedComputeCountAlwaysOne();

        System.out.println("\n-- Warm cache: both compute exactly once sequentially --");
        testDefectiveWarmCacheNoRecompute();
        testFixedWarmCacheNoRecompute();

        System.out.printf("\n%d passed, %d failed%n", passed, failed);
        if (failed > 0) System.exit(1);
    }

    // ── Correctness ───────────────────────────────────────────────────────────

    static void testDefectiveReturnsCorrectValue() {
        Moad0005Algorithm.resetCounter();
        DefectiveCache cache = new DefectiveCache();
        String val = cache.getOrCompute("foo");
        assertEqual("defective: returns 'value-for-foo'", "value-for-foo", val);
    }

    static void testFixedReturnsCorrectValue() {
        Moad0005Algorithm.resetCounter();
        FixedCache cache = new FixedCache();
        String val = cache.getOrCompute("foo");
        assertEqual("fixed: returns 'value-for-foo'", "value-for-foo", val);
    }

    static void testBothReturnSameValue() {
        Moad0005Algorithm.resetCounter();
        DefectiveCache def = new DefectiveCache();
        FixedCache     fix = new FixedCache();
        String dVal = def.getOrCompute("bar");
        Moad0005Algorithm.resetCounter();
        String fVal = fix.getOrCompute("bar");
        assertEqual("both: return same value for 'bar'", dVal, fVal);
    }

    // ── Defect ────────────────────────────────────────────────────────────────

    static void testDefectiveConcurrentMissN10() {
        int computes = Moad0005Algorithm.simulateDefectiveConcurrentMiss(10, "key");
        // DEFECT: all 10 callers see null simultaneously → 10 computes
        assertEqual("defective: 10 concurrent misses cause 10 computes (herd)", 10, computes);
    }

    static void testDefectiveConcurrentMissN50() {
        int computes = Moad0005Algorithm.simulateDefectiveConcurrentMiss(50, "key");
        // DEFECT: 50 concurrent misses → 50 computes
        assertEqual("defective: 50 concurrent misses cause 50 computes (herd)", 50, computes);
    }

    static void testDefectiveComputeCountScalesWithCallers() {
        int c10 = Moad0005Algorithm.simulateDefectiveConcurrentMiss(10, "key");
        int c20 = Moad0005Algorithm.simulateDefectiveConcurrentMiss(20, "key");
        // DEFECT: compute count scales linearly with caller count (N wasted computes)
        assertTrue("defective: doubling callers doubles computes",
            c20 == 2 * c10, "c10=" + c10 + " c20=" + c20);
    }

    // ── Fix ───────────────────────────────────────────────────────────────────

    static void testFixedConcurrentMissN10() {
        int computes = Moad0005Algorithm.simulateFixedConcurrentMiss(10, "key");
        // FIX: computeIfAbsent — exactly 1 compute regardless of caller count
        assertEqual("fixed: 10 concurrent misses cause exactly 1 compute", 1, computes);
    }

    static void testFixedConcurrentMissN50() {
        int computes = Moad0005Algorithm.simulateFixedConcurrentMiss(50, "key");
        assertEqual("fixed: 50 concurrent misses cause exactly 1 compute", 1, computes);
    }

    static void testFixedComputeCountAlwaysOne() {
        int c10  = Moad0005Algorithm.simulateFixedConcurrentMiss(10,  "key");
        int c100 = Moad0005Algorithm.simulateFixedConcurrentMiss(100, "key");
        // FIX: compute count does not scale — always 1
        assertEqual("fixed: 10 callers — 1 compute",   1, c10);
        assertEqual("fixed: 100 callers — 1 compute",  1, c100);
    }

    // ── Warm cache ────────────────────────────────────────────────────────────

    static void testDefectiveWarmCacheNoRecompute() {
        Moad0005Algorithm.resetCounter();
        DefectiveCache cache = new DefectiveCache();
        cache.getOrCompute("warm"); // cold miss — 1 compute
        int afterFirst = Moad0005Algorithm.COMPUTE_CALLS.get();
        cache.getOrCompute("warm"); // warm hit — 0 compute
        int afterSecond = Moad0005Algorithm.COMPUTE_CALLS.get();
        assertEqual("defective: first call computes once",     1, afterFirst);
        assertEqual("defective: second sequential call hits cache", 1, afterSecond);
    }

    static void testFixedWarmCacheNoRecompute() {
        Moad0005Algorithm.resetCounter();
        FixedCache cache = new FixedCache();
        cache.getOrCompute("warm"); // cold miss — 1 compute
        int afterFirst = Moad0005Algorithm.COMPUTE_CALLS.get();
        cache.getOrCompute("warm"); // warm hit — 0 compute
        int afterSecond = Moad0005Algorithm.COMPUTE_CALLS.get();
        assertEqual("fixed: first call computes once",          1, afterFirst);
        assertEqual("fixed: second sequential call hits cache", 1, afterSecond);
    }

    // ── Helpers ───────────────────────────────────────────────────────────────

    static void assertEqual(String label, int expected, int actual) {
        if (expected == actual) {
            System.out.printf("  PASS: %s%n", label);
            passed++;
        } else {
            System.out.printf("  FAIL: %s — expected %d, got %d%n", label, expected, actual);
            failed++;
        }
    }

    static void assertEqual(String label, String expected, String actual) {
        if (expected == null ? actual == null : expected.equals(actual)) {
            System.out.printf("  PASS: %s%n", label);
            passed++;
        } else {
            System.out.printf("  FAIL: %s — expected '%s', got '%s'%n", label, expected, actual);
            failed++;
        }
    }

    static void assertTrue(String label, boolean condition, String detail) {
        if (condition) {
            System.out.printf("  PASS: %s%n", label);
            passed++;
        } else {
            System.out.printf("  FAIL: %s — %s%n", label, detail);
            failed++;
        }
    }
}