C#自定义事件未激发

我正在为Selenium Webdriver编写一个简单的扩展库。我有我的"包装器"类WebDriverManager，它定义事件委托如下：

    public delegate void OnStartEventHandler();
    public delegate void OnTerminateEventHandler();
    public delegate void OnCheckpointEventHandler();
    public event OnStartEventHandler OnStartTesting;
    public event OnTerminateEventHandler OnTerminateTesting;
    public event OnCheckpointEventHandler OnCheckpointTesting;
    /// <summary>
    /// Method that should be fired inside method with [OneTimeSetUp] attribute
    /// </summary>
    public void OnStart() { if (OnStartTesting != null) OnStartTesting(); }
    /// <summary>
    /// Method that should be fired inside method with [OneTimeTearDown] attribute
    /// </summary>
    public void OnTerminate() { if (OnTerminateTesting != null) OnTerminateTesting(); }
    /// <summary>
    /// Method that should be fired inside method with either [SetUp] or [TearDown] attribute
    /// </summary>
    public void OnCheckpoint() { if (OnCheckpointTesting != null) OnCheckpointTesting(); }

在我的目标项目中，我添加了一个对包含WebDriverManager类的库的引用，并编写了一个简单的方法：

    [OneTimeSetUp]
    public void SetUp()
    {
        // wdmChrome and wdmFirefox are instances of WebDriverManager
        wdmChrome.OnStartTesting += () => { Console.WriteLine("Starting testing Chrome browser"); };
        wdmFirefox.OnStartTesting += () => { Console.WriteLine("Starting testing Firefox browser"); };
        wdmChrome.OnTerminateTesting += () => { Console.WriteLine("Terminating test of Chrome browser"); };
        wdmFirefox.OnTerminateTesting += () => { Console.WriteLine("Terminating test of Firefox browser"); };
        wdmChrome.OnStart();
        wdmFirefox.OnStart();
        // other stuff that initializes webdriver
    }
    [OneTimeTearDown]
    public void TearDown()
    {
        wdmChrome.OnTerminate();
        wdmFirefox.OnTerminate();
        wdmChrome.WebDriver.Close();
        wdmFirefox.WebDriver.Close();
    }

测试正常启动并通过，但在"输出"中没有来自委托的消息。我还尝试按照Visual Studio的建议将OnStart()的主体更改为OnStartTesting?.Invoke()，但结果并没有改变。怎么回事？