如何在ASP.NET Core中使用ILogger进行单元测试

这是我的控制器：

public class BlogController : Controller
{
    private IDAO<Blog> _blogDAO;
    private readonly ILogger<BlogController> _logger;

    public BlogController(ILogger<BlogController> logger, IDAO<Blog> blogDAO)
    {
        this._blogDAO = blogDAO;
        this._logger = logger;
    }
    public IActionResult Index()
    {
        var blogs = this._blogDAO.GetMany();
        this._logger.LogInformation("Index page say hello", new object[0]);
        return View(blogs);
    }
}

如您所见，我有2个依赖项，a IDAO和aILogger

这是我的测试类，我使用xUnit进行测试，使用Moq创建模拟和存根，我可以DAO轻松进行模拟，但是由于ILogger我不知道要做什么，所以我只传递了null并注释掉了登录控制器的调用运行测试时。有什么方法可以测试，但仍然以某种方式保持记录器？

public class BlogControllerTest
{
    [Fact]
    public void Index_ReturnAViewResult_WithAListOfBlog()
    {
        var mockRepo = new Mock<IDAO<Blog>>();
        mockRepo.Setup(repo => repo.GetMany(null)).Returns(GetListBlog());
        var controller = new BlogController(null,mockRepo.Object);

        var result = controller.Index();

        var viewResult = Assert.IsType<ViewResult>(result);
        var model = Assert.IsAssignableFrom<IEnumerable<Blog>>(viewResult.ViewData.Model);
        Assert.Equal(2, model.Count());
    }
}

只是模拟它以及任何其他依赖项：

var mock = new Mock<ILogger<BlogController>>();
ILogger<BlogController> logger = mock.Object;

//or use this short equivalent 
logger = Mock.Of<ILogger<BlogController>>()

var controller = new BlogController(logger);

您可能需要安装Microsoft.Extensions.Logging.Abstractions软件包才能使用ILogger<T>。

此外，您可以创建一个真正的记录器：

var serviceProvider = new ServiceCollection()
    .AddLogging()
    .BuildServiceProvider();

var factory = serviceProvider.GetService<ILoggerFactory>();

var logger = factory.CreateLogger<BlogController>();

实际上，我发现Microsoft.Extensions.Logging.Abstractions.NullLogger<>这看起来是一个完美的解决方案。安装软件包Microsoft.Extensions.Logging.Abstractions，然后按照示例进行配置和使用：

using Microsoft.Extensions.Logging;

public void ConfigureServices(IServiceCollection services)
{
    ...

    services.AddSingleton<ILoggerFactory, NullLoggerFactory>();

    ...
}

using Microsoft.Extensions.Logging;

public class MyClass : IMyClass
{
    public const string ErrorMessageILoggerFactoryIsNull = "ILoggerFactory is null";

    private readonly ILogger<MyClass> logger;

    public MyClass(ILoggerFactory loggerFactory)
    {
        if (null == loggerFactory)
        {
            throw new ArgumentNullException(ErrorMessageILoggerFactoryIsNull, (Exception)null);
        }

        this.logger = loggerFactory.CreateLogger<MyClass>();
    }
}

和单元测试

//using Microsoft.VisualStudio.TestTools.UnitTesting;
//using Microsoft.Extensions.Logging;

[TestMethod]
public void SampleTest()
{
    ILoggerFactory doesntDoMuch = new Microsoft.Extensions.Logging.Abstractions.NullLoggerFactory();
    IMyClass testItem = new MyClass(doesntDoMuch);
    Assert.IsNotNull(testItem);
}   

使用自定义记录器，该记录器使用ITestOutputHelper（来自xunit）捕获输出和日志。以下是一个仅将写入state输出的小示例。

public class XunitLogger<T> : ILogger<T>, IDisposable
{
    private ITestOutputHelper _output;

    public XunitLogger(ITestOutputHelper output)
    {
        _output = output;
    }
    public void Log<TState>(LogLevel logLevel, EventId eventId, TState state, Exception exception, Func<TState, Exception, string> formatter)
    {
        _output.WriteLine(state.ToString());
    }

    public bool IsEnabled(LogLevel logLevel)
    {
        return true;
    }

    public IDisposable BeginScope<TState>(TState state)
    {
        return this;
    }

    public void Dispose()
    {
    }
}

在您的单元测试中使用它，例如

public class BlogControllerTest
{
  private XunitLogger<BlogController> _logger;

  public BlogControllerTest(ITestOutputHelper output){
    _logger = new XunitLogger<BlogController>(output);
  }

  [Fact]
  public void Index_ReturnAViewResult_WithAListOfBlog()
  {
    var mockRepo = new Mock<IDAO<Blog>>();
    mockRepo.Setup(repo => repo.GetMany(null)).Returns(GetListBlog());
    var controller = new BlogController(_logger,mockRepo.Object);
    // rest
  }
}

对于使用Moq的.net core 3答案

• https://stackoverflow.com/a/54646657/2164198
• https://stackoverflow.com/a/54809607/2164198

• https://stackoverflow.com/a/56728528/2164198

  由于ILogger中的问题TState中描述的更改而不再起作用。Log以前是对象，现在是FormattedLogValues

幸运的是，stakx提供了一个不错的解决方法。因此，我将其发布，希望它可以为其他人节省时间（花了一些时间才弄清楚）：

 loggerMock.Verify(
                x => x.Log(
                    LogLevel.Information,
                    It.IsAny<EventId>(),
                    It.Is<It.IsAnyType>((o, t) => string.Equals("Index page say hello", o.ToString(), StringComparison.InvariantCultureIgnoreCase)),
                    It.IsAny<Exception>(),
                    (Func<It.IsAnyType, Exception, string>) It.IsAny<object>()),
                Times.Once);

加上我的2美分，这是通常在静态helper类中放入的helper扩展方法：

static class MockHelper
{
    public static ISetup<ILogger<T>> MockLog<T>(this Mock<ILogger<T>> logger, LogLevel level)
    {
        return logger.Setup(x => x.Log(level, It.IsAny<EventId>(), It.IsAny<object>(), It.IsAny<Exception>(), It.IsAny<Func<object, Exception, string>>()));
    }

    private static Expression<Action<ILogger<T>>> Verify<T>(LogLevel level)
    {
        return x => x.Log(level, 0, It.IsAny<object>(), It.IsAny<Exception>(), It.IsAny<Func<object, Exception, string>>());
    }

    public static void Verify<T>(this Mock<ILogger<T>> mock, LogLevel level, Times times)
    {
        mock.Verify(Verify<T>(level), times);
    }
}

然后，您可以像这样使用它：

//Arrange
var logger = new Mock<ILogger<YourClass>>();
logger.MockLog(LogLevel.Warning)

//Act

//Assert
logger.Verify(LogLevel.Warning, Times.Once());

当然，您可以轻松地扩展它以模拟任何期望（即期望，消息等）。

正如其他答案建议通过模拟一样ILogger，这很容易，但是突然之间，要验证是否确实对记录器进行了调用就变得更加困难。原因是大多数调用实际上并不属于ILogger接口本身。

因此，最多的调用是仅调用扩展方法的扩展方法 Log接口方法。看来原因是，如果只有一个重载归结为同一方法，而没有很多重载，则可以更轻松地实现接口。

缺点当然是，由于要验证的呼叫与您发出的呼叫有很大不同，因此突然很难验证是否已进行呼叫。有多种解决方法，我发现模拟框架的自定义扩展方法将使其最容易编写。

这是我使用过的一种方法的示例NSubstitute：

public static class LoggerTestingExtensions
{
    public static void LogError(this ILogger logger, string message)
    {
        logger.Log(
            LogLevel.Error,
            0,
            Arg.Is<FormattedLogValues>(v => v.ToString() == message),
            Arg.Any<Exception>(),
            Arg.Any<Func<object, Exception, string>>());
    }

}

这是可以使用的方式：

_logger.Received(1).LogError("Something bad happened");   

看起来就像您直接使用该方法一样，这里的窍门是我们的扩展方法获得了优先级，因为它在名称空间中比原始方法“更紧密”，因此将使用它。

不幸的是，它不能给出我们想要的100％，即错误消息不会那么好，因为我们不直接检查字符串，而是检查包含该字符串的lambda，但是95％总比没有好：)这种方法将使测试代码

PS对于起订量可以使用写扩展方法的方法了Mock<ILogger<T>>，做Verify来实现类似的结果。

PPS这在.Net Core 3中不再起作用，请检查此线程以获取更多详细信息：https : //github.com/nsubstitute/NSubstitute/issues/597#issuecomment-573742574

已经提到您可以像其他任何接口一样模拟它。

var logger = new Mock<ILogger<QueuedHostedService>>();

到目前为止，一切都很好。

不错的是，您可以Moq用来验证是否已执行某些呼叫。例如，在这里，我检查是否已使用特定的调用了日志Exception。

logger.Verify(m => m.Log(It.Is<LogLevel>(l => l == LogLevel.Information), 0,
            It.IsAny<object>(), It.IsAny<TaskCanceledException>(), It.IsAny<Func<object, Exception, string>>()));

使用Verify该点时，是针对接口的实际Log方法ILooger而不是扩展方法。

这是在@ ivan-samygin和@stakx的工作基础上进一步发展的方法，这些扩展方法也可以在Exception和所有日志值（KeyValuePairs）上匹配。

这些可以在.Net Core 3，Moq 4.13.0和Microsoft.Extensions.Logging.Abstractions 3.1.0中使用（在我的机器上）。

/// <summary>
/// Verifies that a Log call has been made, with the given LogLevel, Message and optional KeyValuePairs.
/// </summary>
/// <typeparam name="T">Type of the class for the logger.</typeparam>
/// <param name="loggerMock">The mocked logger class.</param>
/// <param name="expectedLogLevel">The LogLevel to verify.</param>
/// <param name="expectedMessage">The Message to verify.</param>
/// <param name="expectedValues">Zero or more KeyValuePairs to verify.</param>
public static void VerifyLog<T>(this Mock<ILogger<T>> loggerMock, LogLevel expectedLogLevel, string expectedMessage, params KeyValuePair<string, object>[] expectedValues)
{
    loggerMock.Verify(mock => mock.Log(
        expectedLogLevel,
        It.IsAny<EventId>(),
        It.Is<It.IsAnyType>((o, t) => MatchesLogValues(o, expectedMessage, expectedValues)),
        It.IsAny<Exception>(),
        It.IsAny<Func<object, Exception, string>>()
        )
    );
}

/// <summary>
/// Verifies that a Log call has been made, with LogLevel.Error, Message, given Exception and optional KeyValuePairs.
/// </summary>
/// <typeparam name="T">Type of the class for the logger.</typeparam>
/// <param name="loggerMock">The mocked logger class.</param>
/// <param name="expectedMessage">The Message to verify.</param>
/// <param name="expectedException">The Exception to verify.</param>
/// <param name="expectedValues">Zero or more KeyValuePairs to verify.</param>
public static void VerifyLog<T>(this Mock<ILogger<T>> loggerMock, string expectedMessage, Exception expectedException, params KeyValuePair<string, object>[] expectedValues)
{
    loggerMock.Verify(logger => logger.Log(
        LogLevel.Error,
        It.IsAny<EventId>(),
        It.Is<It.IsAnyType>((o, t) => MatchesLogValues(o, expectedMessage, expectedValues)),
        It.Is<Exception>(e => e == expectedException),
        It.Is<Func<It.IsAnyType, Exception, string>>((o, t) => true)
    ));
}

private static bool MatchesLogValues(object state, string expectedMessage, params KeyValuePair<string, object>[] expectedValues)
{
    const string messageKeyName = "{OriginalFormat}";

    var loggedValues = (IReadOnlyList<KeyValuePair<string, object>>)state;

    return loggedValues.Any(loggedValue => loggedValue.Key == messageKeyName && loggedValue.Value.ToString() == expectedMessage) &&
           expectedValues.All(expectedValue => loggedValues.Any(loggedValue => loggedValue.Key == expectedValue.Key && loggedValue.Value == expectedValue.Value));
}

当使用StructureMap / Lamar时：

var c = new Container(_ =>
{
    _.For(typeof(ILogger<>)).Use(typeof(NullLogger<>));
});

文件：

• https://docs.microsoft.com/zh-cn/dotnet/api/microsoft.extensions.logging.abstractions.nulllogger?view=aspnetcore-2.1
• http://structuremap.github.io/generics/

仅创建一个虚拟ILogger对象对于单元测试不是很有价值。您还应该验证是否进行了日志记录调用。您可以ILogger使用Moq注入模拟，但验证通话可能会有些棘手。本文深入探讨了用Moq进行验证。

这是文章中一个非常简单的示例：

_loggerMock.Verify(l => l.Log(
LogLevel.Information,
It.IsAny<EventId>(),
It.IsAny<It.IsAnyType>(),
It.IsAny<Exception>(),
(Func<It.IsAnyType, Exception, string>)It.IsAny<object>()), Times.Exactly(1));

它验证是否已记录信息消息。但是，如果我们要验证有关消息的更复杂的信息（例如消息模板和命名属性），则会变得更加棘手：

_loggerMock.Verify
(
    l => l.Log
    (
        //Check the severity level
        LogLevel.Error,
        //This may or may not be relevant to your scenario
        It.IsAny<EventId>(),
        //This is the magical Moq code that exposes internal log processing from the extension methods
        It.Is<It.IsAnyType>((state, t) =>
            //This confirms that the correct log message was sent to the logger. {OriginalFormat} should match the value passed to the logger
            //Note: messages should be retrieved from a service that will probably store the strings in a resource file
            CheckValue(state, LogTest.ErrorMessage, "{OriginalFormat}") &&
            //This confirms that an argument with a key of "recordId" was sent with the correct value
            //In Application Insights, this will turn up in Custom Dimensions
            CheckValue(state, recordId, nameof(recordId))
    ),
    //Confirm the exception type
    It.IsAny<NotImplementedException>(),
    //Accept any valid Func here. The Func is specified by the extension methods
    (Func<It.IsAnyType, Exception, string>)It.IsAny<object>()),
    //Make sure the message was logged the correct number of times
    Times.Exactly(1)
);

我确定您可以对其他模拟框架执行相同的操作，但是该ILogger接口确保了这一点很困难。

如果仍然是实际的。在.net Core> = 3的测试中记录日志以输出的简单方法

[Fact]
public void SomeTest()
{
    using var logFactory = LoggerFactory.Create(builder => builder.AddConsole());
    var logger = logFactory.CreateLogger<AccountController>();
    
    var controller = new SomeController(logger);

    var result = controller.SomeActionAsync(new Dto{ ... }).GetAwaiter().GetResult();
}

使用Telerik Just Mock创建记录器的模拟实例：

using Telerik.JustMock;
...
context = new XDbContext(Mock.Create<ILogger<XDbContext>>());

我曾尝试使用NSubstitute模拟Logger接口（并失败，因为Arg.Any<T>()重新输入了我无法提供的类型参数），但最终以以下方式创建了测试记录器（类似于@jehof的答案）：

    internal sealed class TestLogger<T> : ILogger<T>, IDisposable
    {
        private readonly List<LoggedMessage> _messages = new List<LoggedMessage>();

        public IReadOnlyList<LoggedMessage> Messages => _messages;

        public void Dispose()
        {
        }

        public IDisposable BeginScope<TState>(TState state)
        {
            return this;
        }

        public bool IsEnabled(LogLevel logLevel)
        {
            return true;
        }

        public void Log<TState>(LogLevel logLevel, EventId eventId, TState state, Exception exception, Func<TState, Exception, string> formatter)
        {
            var message = formatter(state, exception);
            _messages.Add(new LoggedMessage(logLevel, eventId, exception, message));
        }

        public sealed class LoggedMessage
        {
            public LogLevel LogLevel { get; }
            public EventId EventId { get; }
            public Exception Exception { get; }
            public string Message { get; }

            public LoggedMessage(LogLevel logLevel, EventId eventId, Exception exception, string message)
            {
                LogLevel = logLevel;
                EventId = eventId;
                Exception = exception;
                Message = message;
            }
        }
    }

您可以轻松访问所有记录的消息并声明其随附的所有有意义的参数。