用玩笑測試 promise 拒絕代碼路徑

Question

我有一種情況，當 promise 拒絕時，我正在嘗試測試代碼路徑。 設置相對復雜，但我已將其簡化為最小可重現示例：

let resolver;
let rejecter;

const p = new Promise((resolve, reject) => {
    resolver = resolve;
    rejecter = reject;
});

const f = jest.fn((x) => {
    console.log(x);
});

const run = () => {
    return p
        .then(() => {
            f("resolved");
        })
        .catch(() => {
            f("rejected");
        });
};

beforeEach(() => {
    f.mockClear();
});

// this test passes
test("it should call with resolved when p resolves", async () => {
    run();
    resolver();
    await p;

    expect(f).toHaveBeenCalledWith("resolved");
});

// this test fails
test("it should call with rejected when p rejects", async () => {
    run();
    rejecter();
    await p;

    expect(f).toHaveBeenCalledWith("rejected");
});

我的問題是，盡管f確實被稱為"rejected" ，但測試失敗了，原因是

thrown: undefined

我在這一點上的猜測是，這與 promise 拒絕的事實有關。 我曾希望這不會是一個問題，因為它被抓住了。 我怎樣才能成功完成這個測試？

Answer 1

我通過在 promise p上添加一個catch來解決這個問題：

// this test fails
test("it should call with rejected when p rejects", async () => {
    run();
    rejecter();
    await p.catch(() => {});

    expect(f).toHaveBeenCalledWith("rejected");
});