cjk-autospace/test/observer-recovery.test.mjs

import assert from "node:assert/strict";
import { test } from "node:test";

import { createJuzhen } from "../dist/juzhen.mjs";
import { setupDom } from "./helpers.mjs";

const tick = () => new Promise((resolve) => setTimeout(resolve, 0));

function installCountingMutationObserver(
    maxCallbacks = Number.POSITIVE_INFINITY,
    { deferDelivery = false, wrapRecords = (records) => records } = {},
)
{
    const NativeMutationObserver = globalThis.MutationObserver;
    const instances = [];

    class CountingMutationObserver
    {
        constructor(callback)
        {
            this.callback = callback;
            this.observeCount = 0;
            this.disconnectCount = 0;
            this.callbackCount = 0;
            this.pendingRecords = [];
            this.suppressed = false;
            this.inner = new NativeMutationObserver((records) =>
            {
                if (deferDelivery) { this.pendingRecords.push(...records); }
                else { this.deliver(records); }
            });
            instances.push(this);
        }

        deliver(records)
        {
            this.callbackCount += 1;
            if (this.callbackCount > maxCallbacks)
            {
                this.suppressed = true;
                this.inner.disconnect();
                return;
            }
            this.callback(wrapRecords(records), this);
        }

        observe(target, options)
        {
            this.observeCount += 1;
            if (!this.suppressed) { this.inner.observe(target, options); }
        }

        disconnect()
        {
            this.disconnectCount += 1;
            this.inner.disconnect();
        }

        takeRecords()
        {
            return this.inner.takeRecords();
        }
    }

    globalThis.MutationObserver = CountingMutationObserver;
    return {
        instances,
        restore()
        {
            globalThis.MutationObserver = NativeMutationObserver;
        },
    };
}

function installExpectationShiftProbe()
{
    const nativeShift = Array.prototype.shift;
    let calls = 0;
    let work = 0;
    Array.prototype.shift = function ()
    {
        const head = this[0];
        if (head && typeof head === "object" && "target" in head
            && "oldValue" in head && "newValue" in head)
        {
            calls += 1;
            work += this.length;
        }
        return nativeShift.call(this);
    };
    return {
        result: () => ({ calls, work }),
        restore()
        {
            Array.prototype.shift = nativeShift;
        },
    };
}

function installExpectationSpliceProbe()
{
    const nativeSplice = Array.prototype.splice;
    let calls = 0;
    let removed = 0;
    Array.prototype.splice = function (...args)
    {
        const [ start, deleteCount ] = args;
        const head = this[0];
        if (start === 0 && head && typeof head === "object" && "target" in head
            && "oldValue" in head && "newValue" in head)
        {
            calls += 1;
            removed += deleteCount;
        }
        return nativeSplice.apply(this, args);
    };
    return {
        result: () => ({ calls, removed }),
        restore()
        {
            Array.prototype.splice = nativeSplice;
        },
    };
}

function installLayoutHarness(document, withFonts = false)
{
    const NativeResizeObserver = globalThis.ResizeObserver;
    const originalGetClientRects = window.Element.prototype.getClientRects;
    const instances = [];
    let rectsEnabled = true;
    class CapturingResizeObserver
    {
        constructor(callback)
        {
            this.callback = callback;
            this.target = null;
            this.disconnected = false;
            instances.push(this);
        }

        observe(target)
        {
            this.target = target;
        }

        disconnect()
        {
            this.disconnected = true;
        }

        fire()
        {
            this.callback([ { target: this.target } ], this);
        }
    }
    globalThis.ResizeObserver = CapturingResizeObserver;
    window.Element.prototype.getClientRects = function ()
    {
        if (!rectsEnabled) { return []; }
        return [ {
            bottom: 16, height: 16, left: 0, right: 16,
            top: 0, width: 16, x: 0, y: 0,
        } ];
    };
    if (withFonts)
    {
        Object.defineProperty(document, "fonts", {
            configurable: true,
            value: { ready: Promise.resolve() },
        });
    }
    return {
        instances,
        setRectsEnabled(value)
        {
            rectsEnabled = value;
        },
        restore()
        {
            window.Element.prototype.getClientRects = originalGetClientRects;
            if (NativeResizeObserver === undefined) { delete globalThis.ResizeObserver; }
            else { globalThis.ResizeObserver = NativeResizeObserver; }
        },
    };
}

test("observer recovery: synchronous render failure restores later observation", async () =>
{
    const { document } = setupDom('<div id="root"><p lang="zh-Hant">原文，內容。</p></div>');
    const root = document.getElementById("root");
    const paragraph = root.querySelector("p");
    const expected = new Error("isSkipped render failure");
    let throwNext = false;
    const jz = createJuzhen({
        isSkipped()
        {
            if (!throwNext) { return false; }
            throwNext = false;
            throw expected;
        },
    });

    jz.render(root);
    jz.observe(root);
    jz.invalidate(root);
    throwNext = true;
    assert.throws(() => jz.render(root), (error) => error === expected);

    paragraph.textContent = "錯誤後，仍可繼續觀察。";
    await tick();
    await tick();
    jz.disconnect();
    assert.ok(paragraph.querySelector("jz-char"), "之後的 DOM 變化仍自動處理");
    assert.equal(paragraph.textContent, "錯誤後，仍可繼續觀察。");
});

test("observer recovery: mutation callback failure restores a later mutation", async () =>
{
    const { document } = setupDom('<div id="root"><p lang="zh-Hant">原文，內容。</p></div>');
    const root = document.getElementById("root");
    const paragraph = root.querySelector("p");
    const expected = new Error("isSkipped mutation failure");
    const reported = [];
    let throwNext = false;
    const onError = (event) =>
    {
        reported.push(event.error);
        event.preventDefault();
    };
    window.addEventListener("error", onError);
    const jz = createJuzhen({
        isSkipped()
        {
            if (!throwNext) { return false; }
            throwNext = false;
            throw expected;
        },
    });

    try
    {
        jz.render(root);
        jz.observe(root);
        jz.invalidate(root);
        throwNext = true;
        paragraph.textContent = "第一次，觸發錯誤。";
        await tick();
        assert.ok(reported.includes(expected), "MutationObserver 回調錯誤仍照常對外呈現");

        paragraph.textContent = "第二次，恢復處理。";
        await tick();
        await tick();
        assert.ok(paragraph.querySelector("jz-char"), "後續變化仍被觀察");
        assert.equal(paragraph.textContent, "第二次，恢復處理。");
    }
    finally
    {
        jz.disconnect();
        window.removeEventListener("error", onError);
    }
});

test("observer depth: nested render does not resume or observe partial outer changes", async () =>
{
    const { document } = setupDom('<div id="root"><p lang="zh-Hant">嵌套，渲染。</p></div>');
    const counting = installCountingMutationObserver();
    const root = document.getElementById("root");
    const paragraph = root.querySelector("p");
    let reenter = false;
    let jz;

    try
    {
        jz = createJuzhen({
            isSkipped()
            {
                if (reenter)
                {
                    reenter = false;
                    jz.render(paragraph);
                }
                return false;
            },
        });
        jz.render(root);
        jz.observe(root);
        assert.equal(counting.instances.length, 1);

        jz.invalidate(root);
        reenter = true;
        jz.rerender(root);
        const observer = counting.instances[0];
        assert.equal(observer.disconnectCount, 1, "只有最外層 0→1 暫停會 disconnect");
        assert.equal(observer.observeCount, 2, "只有最外層 1→0 恢復會 observe");

        await tick();
        await tick();
        assert.equal(observer.callbackCount, 0, "嵌套處理不會觀察半成品或自觸發");
        assert.ok(paragraph.querySelector("jz-char"));
    }
    finally
    {
        if (jz) { jz.disconnect(); }
        counting.restore();
    }
});

test("observer depth: observe replacement inside a paused render is deferred coherently", async () =>
{
    const { document } = setupDom('<div id="root"><p lang="zh-Hant">重建，觀察。</p></div>');
    const counting = installCountingMutationObserver();
    const root = document.getElementById("root");
    const paragraph = root.querySelector("p");
    let replaceObserver = false;
    let observeCallsDuringPause = -1;
    let jz;

    try
    {
        jz = createJuzhen({
            isSkipped()
            {
                if (replaceObserver)
                {
                    replaceObserver = false;
                    jz.disconnect();
                    jz.observe(root);
                    observeCallsDuringPause = counting.instances.reduce(
                        (sum, observer) => sum + observer.observeCount, 0,
                    );
                }
                return false;
            },
        });
        jz.render(root);
        jz.observe(root);
        jz.invalidate(root);
        replaceObserver = true;
        jz.rerender(root);

        assert.equal(counting.instances.length, 2, "嵌套 observe 建立新觀察者");
        assert.equal(observeCallsDuringPause, 1, "暫停期內新觀察者尚未 observe");
        assert.equal(
            counting.instances.reduce((sum, observer) => sum + observer.observeCount, 0),
            2,
            "最外層結束後新觀察者恰恢復一次",
        );

        paragraph.textContent = "重建後，仍能處理。";
        await tick();
        await tick();
        assert.ok(paragraph.querySelector("jz-char"));
        assert.equal(counting.instances[1].callbackCount, 1, "新觀察者接手後續變化");
    }
    finally
    {
        if (jz) { jz.disconnect(); }
        counting.restore();
    }
});

test("observer provenance: asynchronous internal layout classes do not self-trigger", async () =>
{
    const { document } = setupDom('<div id="root"><p lang="zh-Hant">（版面回調</p></div>');
    const counting = installCountingMutationObserver(8);
    const layout = installLayoutHarness(document, true);
    const root = document.getElementById("root");
    const paragraph = root.querySelector("p");
    let jz;

    try
    {
        jz = createJuzhen({ spacing: false, orphan: false });
        jz.render(root);
        jz.observe(root);

        await tick();
        await tick();

        const observer = counting.instances[0];
        assert.equal(layout.instances.length, 1, "未因內部 class 記錄重建 layout observer");
        assert.equal(observer.callbackCount, 1, "同批 remove/add provenance 被精確消費");
        assert.equal(observer.suppressed, false, "防掛上限未被觸發");
        assert.ok(paragraph.querySelector("jz-char.jz-half-le"), "異步行端結果保持");
    }
    finally
    {
        if (jz) { jz.disconnect(); }
        layout.restore();
        counting.restore();
    }
});

test("observer provenance: author whitelist attributes still trigger rerender", async () =>
{
    const { document } = setupDom('<div id="root"><p lang="zh-Hant">作者，屬性。</p></div>');
    const counting = installCountingMutationObserver();
    const root = document.getElementById("root");
    const paragraph = root.querySelector("p");
    const jz = createJuzhen();
    try
    {
        jz.render(root);
        jz.observe(root);
        paragraph.classList.add("consumer-class");
        await tick();
        assert.equal(counting.instances[0].callbackCount, 1, "作者 class 觸發 observer");
        assert.ok(paragraph.querySelector("jz-char"));

        paragraph.setAttribute("data-jz-skip", "");
        await tick();
        assert.equal(counting.instances[0].callbackCount, 2, "作者非 class 白名單屬性亦觸發");
        assert.equal(paragraph.querySelectorAll("[data-jz]").length, 0, "skip 重分類生效");
    }
    finally
    {
        jz.disconnect();
        counting.restore();
    }
});

test("observer provenance: external writes on owned products are not consumed", async () =>
{
    const { document } = setupDom('<div id="root"><p lang="zh-Hans">前文<strong>粗体文字</strong>，后续</p></div>');
    const counting = installCountingMutationObserver();
    const root = document.getElementById("root");
    const jz = createJuzhen({ spacing: false, longWord: false, orphan: false });
    try
    {
        jz.render(root);
        jz.observe(root);

        const atom = root.querySelector("jz-char");
        atom.classList.add("consumer-class");
        await tick();
        assert.equal(counting.instances[0].callbackCount, 1, "owned 元素外部 class 觸發");
        assert.equal(atom.isConnected, false, "外部 class 變更進入 rerender");

        const nextAtom = root.querySelector("jz-char");
        nextAtom.setAttribute("lang", "en");
        await tick();
        assert.equal(counting.instances[0].callbackCount, 2, "owned 元素外部 lang 觸發");
        assert.equal(nextAtom.isConnected, false);

        const splitoff = root.querySelector('[data-jz-kind="splitoff"]');
        splitoff.classList.add("consumer-splitoff");
        await tick();
        assert.equal(counting.instances[0].callbackCount, 3, "owned splitoff 外部 class 觸發");
        // 外部樣式使片段無法安全併回；rerender 須保留作者元素與字序，不能丟掉 class。
        assert.equal(splitoff.isConnected, true);
        assert.ok(splitoff.classList.contains("consumer-splitoff"));
        assert.equal(splitoff.hasAttribute("data-jz-kind"), false, "舊 splitoff 憑證已撤銷");
        assert.equal(root.textContent, "前文粗体文字，后续");
        jz.revert(root);
        assert.equal(splitoff.isConnected, true);
        assert.ok(splitoff.classList.contains("consumer-splitoff"));
        assert.equal(root.querySelectorAll("[data-jz]").length, 0);
    }
    finally
    {
        jz.disconnect();
        counting.restore();
    }
});

test("observer provenance: mixed internal and external class records stay distinguishable", async () =>
{
    const { document } = setupDom('<div id="root"><p lang="zh-Hant">（混合記錄</p></div>');
    const counting = installCountingMutationObserver();
    const layout = installLayoutHarness(document);
    const root = document.getElementById("root");
    const jz = createJuzhen({ spacing: false, orphan: false });
    try
    {
        jz.render(root);
        jz.observe(root);
        const atom = root.querySelector("jz-char");
        atom.classList.add("consumer-before-internal");
        layout.instances[0].fire();
        await tick();

        assert.equal(counting.instances[0].callbackCount, 1, "同批記錄只派發一次");
        assert.equal(atom.isConnected, false, "外部 mismatch 後之內部 transition 仍精確消費");
    }
    finally
    {
        jz.disconnect();
        layout.restore();
        counting.restore();
    }
});

test(
    "observer provenance: threshold compaction preserves a 1024-record tail across callbacks",
    { timeout: 20000 },
    async () =>
    {
        const size = 2048;
        const html = Array.from({ length: size }, (_, index) => `<p>（${index}</p>`).join("");
        const { document } = setupDom(`<div id="root" lang="zh-Hant">${html}</div>`);
        const counting = installCountingMutationObserver(4, { deferDelivery: true });
        const layout = installLayoutHarness(document);
        const spliceProbe = installExpectationSpliceProbe();
        const root = document.getElementById("root");
        const jz = createJuzhen({ spacing: false, longWord: false, orphan: false });
        try
        {
            jz.render(root);
            jz.observe(root);
            layout.setRectsEnabled(false);
            layout.instances[0].fire();
            await tick();

            const observer = counting.instances[0];
            const records = observer.pendingRecords.splice(0);
            assert.equal(records.length, size, "每個 target 各排入一條 internal remove");
            observer.deliver(records.slice(0, 1024));
            assert.deepEqual(spliceProbe.result(), { calls: 1, removed: 1024 });
            assert.equal(layout.instances.length, 1, "首批觸發 threshold compaction 而不 rerender");
            observer.deliver(records.slice(1024));
            assert.equal(observer.callbackCount, 2, "第二批由壓縮後 deque 繼續消費");
            assert.equal(layout.instances.length, 1, "尾批全消費後 head/reset 正確");
            assert.equal(root.querySelectorAll("jz-char.jz-half-le").length, 0);
        }
        finally
        {
            jz.disconnect();
            spliceProbe.restore();
            layout.restore();
            counting.restore();
        }
    },
);

test(
    "observer provenance: callback failure compacts the consumed prefix and preserves its tail",
    { timeout: 15000 },
    async () =>
    {
        const size = 1025;
        const html = Array.from({ length: size }, (_, index) => `<p>（${index}</p>`).join("");
        const { document } = setupDom(`<div id="root" lang="zh-Hant">${html}</div>`);
        const counting = installCountingMutationObserver(4, { deferDelivery: true });
        const layout = installLayoutHarness(document);
        const spliceProbe = installExpectationSpliceProbe();
        const root = document.getElementById("root");
        const jz = createJuzhen({ spacing: false, longWord: false, orphan: false });
        const expected = new Error("mid-callback classification failure");
        const throwingRecord = {
            type: "characterData",
            get target()
            {
                throw expected;
            },
        };
        try
        {
            jz.render(root);
            jz.observe(root);
            layout.setRectsEnabled(false);
            layout.instances[0].fire();
            await tick();

            const observer = counting.instances[0];
            const records = observer.pendingRecords.splice(0);
            assert.equal(records.length, size);
            assert.throws(
                () => observer.deliver([ ...records.slice(0, 1024), throwingRecord ]),
                (error) => error === expected,
            );
            assert.deepEqual(
                spliceProbe.result(),
                { calls: 1, removed: 1024 },
                "拋錯 callback 之 finally 立即壓縮已消費前綴",
            );
            assert.equal(layout.instances.length, 1, "finally 壓縮已消費前綴而不 rerender");

            observer.deliver([ records[1024] ]);
            assert.equal(layout.instances.length, 1, "下一 callback 精確消費保留之 tail");

            const atom = root.querySelector("jz-char");
            atom.classList.add("consumer-after-callback-error");
            await tick();
            assert.equal(observer.pendingRecords.length, 1, "外部 class 排入獨立 record");
            observer.deliver(observer.pendingRecords.splice(0));
            assert.equal(observer.callbackCount, 3, "錯誤、tail、外部 record 各交付一次");
            assert.equal(atom.isConnected, false, "外部 record 未被殘留 expectation 誤吞");
        }
        finally
        {
            jz.disconnect();
            spliceProbe.restore();
            layout.restore();
            counting.restore();
        }
    },
);

test("observer provenance: foreign-instance product changes still trigger", async () =>
{
    const { document } = setupDom('<div id="root"><p lang="zh-Hant">外來，產物。</p></div>');
    const foreign = createJuzhen();
    const root = document.getElementById("root");
    foreign.render(root);
    const atom = root.querySelector("jz-char");
    const counting = installCountingMutationObserver();
    const local = createJuzhen();
    try
    {
        local.observe(root);
        atom.classList.add("foreign-change");
        await tick();
        assert.equal(counting.instances[0].callbackCount, 1, "外來實例無本地 provenance");
    }
    finally
    {
        local.disconnect();
        counting.restore();
    }
});

for (const mutationKind of [ "childList", "characterData" ])
{
    test(`observer provenance: owned ${mutationKind} changes still trigger`, async () =>
    {
        const { document } = setupDom('<div id="root"><p lang="zh-Hant">內容，變更。</p></div>');
        const counting = installCountingMutationObserver();
        const root = document.getElementById("root");
        const jz = createJuzhen();
        try
        {
            jz.render(root);
            jz.observe(root);
            const atom = root.querySelector("jz-char");
            if (mutationKind === "childList") { atom.append("外"); }
            else
            {
                const text = document.createTreeWalker(atom, NodeFilter.SHOW_TEXT).nextNode();
                text.data += "外";
            }
            await tick();
            assert.equal(counting.instances[0].callbackCount, 1);
            assert.equal(atom.isConnected, false, `${mutationKind} 進入 rerender`);
        }
        finally
        {
            jz.disconnect();
            counting.restore();
        }
    });
}

for (const lifecycle of [ "pause", "replace", "disconnect" ])
{
    test(`observer provenance: ${lifecycle} clears stale expectations`, async () =>
    {
        const { document } = setupDom('<div id="root"><p lang="zh-Hant">（生命週期</p></div>');
        const counting = installCountingMutationObserver();
        const layout = installLayoutHarness(document);
        const root = document.getElementById("root");
        const jz = createJuzhen({ spacing: false, orphan: false });
        try
        {
            jz.render(root);
            jz.observe(root);
            layout.instances[0].fire();
            if (lifecycle === "pause") { jz.rerender(root); }
            else if (lifecycle === "replace") { jz.observe(root); }
            else { jz.disconnect(); jz.observe(root); }

            const activeObserver = counting.instances[counting.instances.length - 1];
            root.querySelector("jz-char").classList.add("consumer-after-lifecycle");
            await tick();
            assert.equal(activeObserver.callbackCount, 1, "外部 class 未被陳舊 provenance 吞掉");
        }
        finally
        {
            jz.disconnect();
            layout.restore();
            counting.restore();
        }
    });
}

test("observer provenance: transition inference and queue consumption scale linearly", async (context) =>
{
    const reports = [];
    for (const size of [ 500, 1000, 2000 ])
    {
        const html = Array.from({ length: size }, (_, index) => `<p>（${index}</p>`).join("");
        const { document } = setupDom(`<div id="root" lang="zh-Hant">${html}</div>`);
        let recordAccesses = 0;
        let recordCount = 0;
        const counting = installCountingMutationObserver(Number.POSITIVE_INFINITY, {
            wrapRecords(records)
            {
                recordCount += records.length;
                return records.map((record) => new Proxy({}, {
                    get(_target, property)
                    {
                        recordAccesses += 1;
                        return record[property];
                    },
                }));
            },
        });
        const layout = installLayoutHarness(document);
        const shiftProbe = installExpectationShiftProbe();
        const root = document.getElementById("root");
        const jz = createJuzhen({ spacing: false, longWord: false, orphan: false });
        try
        {
            jz.render(root);
            jz.observe(root);
            assert.equal(root.querySelectorAll("jz-char.jz-half-le").length, size);
            layout.instances[0].fire();
            await tick();

            const shift = shiftProbe.result();
            assert.equal(recordCount, size * 2, "每 target 恰有 remove/add 兩條 transition");
            const report = { size, recordCount, recordAccesses, queueShiftWork: shift.work };
            context.diagnostic("linear probe " + JSON.stringify(report));
            assert.ok(
                recordAccesses <= recordCount * 12 && shift.calls === 0 && shift.work === 0,
                "transition 推斷與 queue 消費保持線性：" + JSON.stringify(report),
            );
            assert.equal(layout.instances.length, 1, "規模回放沒有自觸發 rerender");
            reports.push(report);
        }
        finally
        {
            jz.disconnect();
            shiftProbe.restore();
            layout.restore();
            counting.restore();
        }
    }
    context.diagnostic("linear probes complete " + JSON.stringify(reports));
});

test("observer：手動局部操作先結算其他兄弟塊的待交付變更", async () =>
{
    for (const operation of [ "render", "rerender", "revert" ])
    {
        const { dom, document } = setupDom('<main><p id="a">原文，甲。</p><p id="b">原文，乙。</p></main>');
        const root = document.querySelector("main");
        const a = document.getElementById("a");
        const b = document.getElementById("b");
        const jz = createJuzhen({ jinze: false, orphan: false, longWord: false });
        try
        {
            jz.render(root);
            jz.observe(root);
            a.textContent = "改後，新文。";
            jz[operation](b);
            await tick();
            assert.equal(a.querySelectorAll("jz-char").length, 2, operation + " 不丟棄兄弟變更");
            if (operation === "revert") { assert.equal(b.querySelector("[data-jz]"), null); }
            a.textContent = "再次，更新。";
            await tick();
            assert.equal(a.querySelectorAll("jz-char").length, 2, "結算後繼續觀察");
        }
        finally { jz.disconnect(); dom.window.close(); }
    }
});

test("observer：祖先分類待更新時手動 revert 子塊仍最後生效", async () =>
{
    const { dom, document } = setupDom('<main><p id="a">甲文，內容。</p><p id="b">乙文，內容。</p></main>');
    const root = document.querySelector("main");
    const a = document.getElementById("a");
    const b = document.getElementById("b");
    const jz = createJuzhen();
    try
    {
        jz.render(root);
        jz.observe(root);
        root.setAttribute("data-jz-level", "text");
        jz.revert(b);
        await tick();
        assert.equal(a.getAttribute("data-jz-block-level"), "text");
        assert.equal(a.querySelector("jz-orphan"), null, "兄弟塊採新祖先級別");
        assert.equal(b.querySelector("[data-jz]"), null, "舊祖先記錄不重新 render 已回退子塊");
        assert.equal(b.hasAttribute("data-jz-block-level"), false);
    }
    finally { jz.disconnect(); dom.window.close(); }
});

test("observer：暫停前結算失敗仍非同步報錯，不阻擋手動操作及後續觀察", async () =>
{
    const { dom, document } = setupDom('<main><p id="a">甲文，內容。</p><p id="b">乙文，內容。</p></main>');
    const root = document.querySelector("main");
    const a = document.getElementById("a");
    const b = document.getElementById("b");
    const expected = new Error("pending mutation failure");
    let shouldThrow = false;
    const errors = [];
    dom.window.addEventListener("error", (event) =>
    {
        errors.push(event.error);
        event.preventDefault();
    });
    const jz = createJuzhen({
        jinze: false, orphan: false, longWord: false,
        isSkipped(node)
        {
            if (shouldThrow && node === a) { shouldThrow = false; throw expected; }
            return false;
        },
    });
    try
    {
        jz.render(root);
        jz.observe(root);
        a.textContent = "改後，新文。";
        shouldThrow = true;
        assert.doesNotThrow(() => jz.revert(b), "舊 observer 錯誤不變成同步 API 例外");
        assert.equal(errors.length, 0);
        await tick();
        assert.deepEqual(errors, [ expected ]);
        assert.equal(b.querySelector("[data-jz]"), null);
        a.textContent = "再次，更新。";
        await tick();
        assert.equal(a.querySelectorAll("jz-char").length, 2);
    }
    finally { jz.disconnect(); dom.window.close(); }
});