跳至主要内容

模拟浏览器API

简介​

Playwright为大多数浏览器功能提供了原生支持。然而，存在一些实验性API以及尚未被所有浏览器完全支持的API。在这种情况下，Playwright通常不会提供专门的自动化API。您可以使用模拟(mocks)来测试应用程序在这些情况下的行为。本指南提供了一些示例。

简介​

让我们考虑一个使用battery API来显示设备电池状态的网页应用。我们将模拟电池API并检查页面是否正确显示电池状态。

创建模拟​

由于页面可能在加载过程中很早就调用API，因此在页面开始加载之前设置所有模拟非常重要。实现这一点的最简单方法是调用page.addInitScript()：

await page.addInitScript(() => {
  const mockBattery = {
    level: 0.75,
    charging: true,
    chargingTime: 1800,
    dischargingTime: Infinity,
    addEventListener: () => { }
  };
  // Override the method to always return mock battery info.
  window.navigator.getBattery = async () => mockBattery;
});

完成此操作后，您可以导航页面并检查其UI状态：

// Configure mock API before each test.
test.beforeEach(async ({ page }) => {
  await page.addInitScript(() => {
    const mockBattery = {
      level: 0.90,
      charging: true,
      chargingTime: 1800, // seconds
      dischargingTime: Infinity,
      addEventListener: () => { }
    };
    // Override the method to always return mock battery info.
    window.navigator.getBattery = async () => mockBattery;
  });
});

test('show battery status', async ({ page }) => {
  await page.goto('/');
  await expect(page.locator('.battery-percentage')).toHaveText('90%');
  await expect(page.locator('.battery-status')).toHaveText('Adapter');
  await expect(page.locator('.battery-fully')).toHaveText('00:30');
});

模拟只读API​

某些API是只读的，因此您无法为导航器属性赋值。例如，

// Following line will have no effect.
navigator.cookieEnabled = true;

然而，如果该属性是可配置的，你仍然可以使用普通的JavaScript来覆盖它：

await page.addInitScript(() => {
  Object.defineProperty(Object.getPrototypeOf(navigator), 'cookieEnabled', { value: false });
});

验证API调用​

有时检查页面是否完成了所有预期的API调用很有用。您可以记录所有API方法调用，然后将它们与预期结果进行比较。page.exposeFunction()可能有助于将消息从页面传递回测试代码：

test('log battery calls', async ({ page }) => {
  const log = [];
  // Expose function for pushing messages to the Node.js script.
  await page.exposeFunction('logCall', msg => log.push(msg));
  await page.addInitScript(() => {
    const mockBattery = {
      level: 0.75,
      charging: true,
      chargingTime: 1800,
      dischargingTime: Infinity,
      // Log addEventListener calls.
      addEventListener: (name, cb) => logCall(`addEventListener:${name}`)
    };
    // Override the method to always return mock battery info.
    window.navigator.getBattery = async () => {
      logCall('getBattery');
      return mockBattery;
    };
  });

  await page.goto('/');
  await expect(page.locator('.battery-percentage')).toHaveText('75%');

  // Compare actual calls with golden.
  expect(log).toEqual([
    'getBattery',
    'addEventListener:chargingchange',
    'addEventListener:levelchange'
  ]);
});

更新模拟​

为了测试应用程序是否正确反映电池状态更新，确保模拟电池对象触发与浏览器实现相同的事件非常重要。以下测试演示了如何实现这一点：

test('update battery status (no golden)', async ({ page }) => {
  await page.addInitScript(() => {
    // Mock class that will notify corresponding listeners when battery status changes.
    class BatteryMock {
      level = 0.10;
      charging = false;
      chargingTime = 1800;
      dischargingTime = Infinity;
      _chargingListeners = [];
      _levelListeners = [];
      addEventListener(eventName, listener) {
        if (eventName === 'chargingchange')
          this._chargingListeners.push(listener);
        if (eventName === 'levelchange')
          this._levelListeners.push(listener);
      }
      // Will be called by the test.
      _setLevel(value) {
        this.level = value;
        this._levelListeners.forEach(cb => cb());
      }
      _setCharging(value) {
        this.charging = value;
        this._chargingListeners.forEach(cb => cb());
      }
    }
    const mockBattery = new BatteryMock();
    // Override the method to always return mock battery info.
    window.navigator.getBattery = async () => mockBattery;
    // Save the mock object on window for easier access.
    window.mockBattery = mockBattery;
  });

  await page.goto('/');
  await expect(page.locator('.battery-percentage')).toHaveText('10%');

  // Update level to 27.5%
  await page.evaluate(() => window.mockBattery._setLevel(0.275));
  await expect(page.locator('.battery-percentage')).toHaveText('27.5%');
  await expect(page.locator('.battery-status')).toHaveText('Battery');

  // Emulate connected adapter
  await page.evaluate(() => window.mockBattery._setCharging(true));
  await expect(page.locator('.battery-status')).toHaveText('Adapter');
  await expect(page.locator('.battery-fully')).toHaveText('00:30');
});