如何模拟ILogger LogInformation

Question

我有一个接收ILogger的类，我想模拟LogInformation调用，但这是一个扩展方法。如何对此进行适当的设置调用？

Answer 1

如果你使用的是Moq >= 4.13，这里有一种模拟ILogger的方法

logger.Verify(x => x.Log(
    It.IsAny<LogLevel>(),
    It.IsAny<EventId>(),
    It.IsAny<It.IsAnyType>(),
    It.IsAny<Exception>(),
    (Func<It.IsAnyType, Exception, string>)It.IsAny<object>()));

您可以更具体地更改It.IsAny<LogLevel>()、It.IsAny<EventId>()和It.IsAny<Exception>()存根，但必须使用It.IsAnyType，因为FormattedLogValues现在是internal。

参考：TState in ILogger.Log used to be object, now FormattedLogValues

Answer 2

带有回调的示例，使用Moq 4.14.5测试。此Github Issue上提供了更多信息

PM>安装-软件包模式

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

logger.Setup(x => x.Log(
    It.IsAny<LogLevel>(),
    It.IsAny<EventId>(),
    It.IsAny<It.IsAnyType>(),
    It.IsAny<Exception>(),
    (Func<It.IsAnyType, Exception, string>)It.IsAny<object>()))
    .Callback(new InvocationAction(invocation =>
    {
        var logLevel = (LogLevel)invocation.Arguments[0]; // The first two will always be whatever is specified in the setup above
        var eventId = (EventId)invocation.Arguments[1];  // so I'm not sure you would ever want to actually use them
        var state = invocation.Arguments[2];
        var exception = (Exception)invocation.Arguments[3];
        var formatter = invocation.Arguments[4];

        var invokeMethod = formatter.GetType().GetMethod("Invoke");
        var logMessage = (string)invokeMethod?.Invoke(formatter, new[] { state, exception });
    }));

一个完整的UnitTesting泛型助手类

public static class LoggerHelper
{
    public static Mock<ILogger<T>> GetLogger<T>()
    {
        var logger = new Mock<ILogger<T>>();

        logger.Setup(x => x.Log(
            It.IsAny<LogLevel>(),
            It.IsAny<EventId>(),
            It.IsAny<It.IsAnyType>(),
            It.IsAny<Exception>(),
            (Func<It.IsAnyType, Exception, string>)It.IsAny<object>()))
            .Callback(new InvocationAction(invocation =>
            {
                var logLevel = (LogLevel)invocation.Arguments[0]; // The first two will always be whatever is specified in the setup above
                var eventId = (EventId)invocation.Arguments[1];  // so I'm not sure you would ever want to actually use them
                var state = invocation.Arguments[2];
                var exception = (Exception)invocation.Arguments[3];
                var formatter = invocation.Arguments[4];

                var invokeMethod = formatter.GetType().GetMethod("Invoke");
                var logMessage = (string)invokeMethod?.Invoke(formatter, new[] { state, exception });

                Trace.WriteLine($"{logLevel} - {logMessage}");
            }));

        return logger;
    }
}

Answer 3

通常通过扩展方法、LogWarning、LogError等使用ILogger。

在我的例子中，我感兴趣的是LogWarning方法，在查看代码之后，它将调用ILogger中的Log方法。为了用Moq模拟它，这就是我最终要做的：

     var list = new List<string>();
                var logger = new Mock<ILogger>();
                logger
                    .Setup(l => l.Log<FormattedLogValues>(LogLevel.Warning, It.IsAny<EventId>(), It.IsAny<FormattedLogValues>(), It.IsAny<Exception>(), It.IsAny<Func<FormattedLogValues, Exception, string>>()))
                    .Callback(
                    delegate (LogLevel logLevel, EventId eventId, FormattedLogValues state, Exception exception, Func<FormattedLogValues, Exception, string> formatter)
                    {
                        list.Add(state.ToString());
                    });

在较新版本的.NET Core3.0中，这将不起作用。因为FormattedLogValues是一个内部类型。您需要将moq版本至少更新为：

`<PackageReference Include="Moq" Version="4.16.0" />`

更新Moq后，解决方法如下所示：

            var log = new List<string>();
            var mockLogger = new Mock<ILogger>();
            mockLogger.Setup(
                l => l.Log(
                    It.IsAny<LogLevel>(),
                    It.IsAny<EventId>(),
                    It.IsAny<It.IsAnyType>(),
                    It.IsAny<Exception>(),
                    (Func<It.IsAnyType, Exception, string>)It.IsAny<object>()))
                .Callback((IInvocation invocation) =>
                {
                    var logLevel = (LogLevel)invocation.Arguments[0];
                    var eventId = (EventId)invocation.Arguments[1];
                    var state = (IReadOnlyCollection<KeyValuePair<string, object>>)invocation.Arguments[2];
                    var exception = invocation.Arguments[3] as Exception;
                    var formatter = invocation.Arguments[4] as Delegate;
                    var formatterStr = formatter.DynamicInvoke(state, exception);
                    log.Add(
                      $"{logLevel} - {eventId.Id} - Testing - {formatterStr}");
                });

注意特殊的类型转换：(Func<It.IsAnyType, Exception, string>)It.IsAny<object>())和处理参数的IInvocation。