如何对 Serilog 的 LogContext 属性进行单元测试

Question

我们有一个相当简单netstandard2.0的自定义中间件项目，它使用 Serilog 的静态 LogContext 将指定的 HttpContext 标头复制到日志上下文。

我正在尝试编写一个单元测试，在其中设置一个使用 aDelegatingSink写入变量的记录器。然后它执行Invoke()中间件方法。然后我尝试使用该事件来断言已添加的属性。到目前为止，中间件添加的属性没有显示，但我在测试中添加的属性显示了。我假设它正在处理不同的上下文，但我不确定如何解决这个问题。我尝试了几种不同的方法，但都没有奏效。

由于LogContext是静态的，我认为这会很简单，但我低估了一些东西。这就是我现在所处的位置（为简洁起见省略了一些代码）。我做了确认LogContext.PushProperty中间件的线是被击中在运行时休息。

考试：

...
[Fact]
public async Task Adds_WidgetId_To_LogContext()
{
    LogEvent lastEvent = null;

    var log = new LoggerConfiguration()
        .Enrich.FromLogContext()
        .WriteTo.Sink(new DelegatingSink(e => lastEvent = e))
        .CreateLogger();
         // tried with and without this, also tried the middleware class name
        //.ForContext<HttpContextCorrelationHeadersLoggingMiddlewareTests>(); 

    var context = await GetInvokedContext().ConfigureAwait(false);

    LogContext.PushProperty("MyTestProperty", "my-value");

    log.Information("test");

    // At this point, 'lastEvent' only has the property "MyTestProperty" :(
}

private async Task<DefaultHttpContext> GetInvokedContext(bool withHeaders = true)
{
    RequestDelegate next = async (innerContext) =>
        await innerContext.Response
            .WriteAsync("Test response.")
            .ConfigureAwait(false);

    var middleware = new MyCustomMiddleware(next, _options);

    var context = new DefaultHttpContext();

    if (withHeaders)
    {
        context.Request.Headers.Add(_options.WidgetIdKey, _widgetId);
    }

    await middleware.Invoke(context).ConfigureAwait(false);

    return context;
}

中间件（测试项目引用此项目）：

...
public async Task Invoke(HttpContext context)
{
    if (context == null || context.Request.Headers.Count == 0) { await _next(context).ConfigureAwait(false); }

    var headers = context.Request.Headers;

    foreach (var keyName in KeyNames)
    {
        if (headers.ContainsKey(keyName))
        {
            LogContext.PushProperty(keyName, headers[keyName]);
        }
    }

    await _next(context).ConfigureAwait(false);
}
...

这是我从 Serilog 测试源中偷来的委托接收器：

public class DelegatingSink : ILogEventSink
{
    readonly Action<LogEvent> _write;

    public DelegatingSink(Action<LogEvent> write)
    {
        _write = write ?? throw new ArgumentNullException(nameof(write));
    }

    public void Emit(LogEvent logEvent)
    {
        _write(logEvent);
    }

    public static LogEvent GetLogEvent(Action<ILogger> writeAction)
    {
        LogEvent result = null;

        var l = new LoggerConfiguration()
            .WriteTo.Sink(new DelegatingSink(le => result = le))
            .CreateLogger();

        writeAction(l);

        return result;
    }
}

Answer 1

我还必须对记录的事件的推送属性进行单元测试。假设您正在推动您的财产如下：

public async Task<T> FooAsync(/*...*/)
{
     /*...*/
     using (LogContext.PushProperty("foo", "bar"))
     {
         Log.Information("foobar");
     }
     /*...*/
}

您可以像本示例一样使用Serilog.Sinks.TestCorrelator作为专用于测试的 Serilog 接收器对其进行单元测试（我也在这里使用NUnit和FluentAssertion ）：

[Test]
public async Task Should_assert_something()
{
    ///Arrange
    // I had issues with unit test seeing log events from other tests running at the same time so I recreate context in each test now
    using (TestCorrelator.CreateContext())
    using (var logger = new LoggerConfiguration().WriteTo.Sink(new TestCorrelatorSink()).Enrich.FromLogContext().CreateLogger())
    {
        Log.Logger = logger;
        /*...*/
        /// Act
        var xyz = await FooAsync(/*...*/)
        /*...*/

        /// Assert 
        TestCorrelator.GetLogEventsFromCurrentContext().Should().ContainSingle().Which.MessageTemplate.Text.Should().Be("foobar");
    }
}