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Easily check ILogger<T> interactions with ASP.NET Core Logging and Moq
using Microsoft.Extensions.Logging;
using Moq;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Xunit;
namespace Knaap.Utilties
{
public class SimpleLogCheck
{
[Fact]
public void TestLog()
{
var loggerMock = LoggerUtils.LoggerMock<SimpleLogCheck>();
loggerMock.Object.LogInformation("test");
loggerMock.VerifyLog(LogLevel.Information, "test");
}
}
public static class LoggerUtils
{
public static Mock<ILogger<T>> LoggerMock<T>() where T : class
{
return new Mock<ILogger<T>>();
}
/// <summary>
/// Returns an <pre>ILogger<T></pre> as used by the Microsoft.Logging framework.
/// You can use this for constructors that require an ILogger parameter.
/// </summary>
/// <typeparam name="T"></typeparam>
/// <returns></returns>
public static ILogger<T> Logger<T>() where T : class
{
return LoggerMock<T>().Object;
}
public static void VerifyLog<T>(this Mock<ILogger<T>> loggerMock, LogLevel level, string message, string failMessage = null)
{
loggerMock.VerifyLog(level, message, Times.Once(), failMessage);
}
public static void VerifyLog<T>(this Mock<ILogger<T>> loggerMock, LogLevel level, string message, Times times, string failMessage = null)
{
loggerMock.Verify(l => l.Log<Object>(level, It.IsAny<EventId>(), It.Is<Object>(o => o.ToString() == message), null, It.IsAny<Func<Object, Exception, String>>()), times, failMessage);
}
}
}
@robert-fahey

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@robert-fahey robert-fahey commented Mar 19, 2020

Didn't work for me

Moq.MockException :
Expected invocation on the mock once, but was 0 times: l => l.Log(LogLevel.Information, It.IsAny(), It.Is(o => o.ToString() == "test"), null, It.IsAny<Func<object, Exception, string>>())

Performed invocations:

Mock<ILogger:1> (l):

  ILogger.Log<FormattedLogValues>(LogLevel.Information, 0, test, null, Func<FormattedLogValues, Exception, string>)

at Moq.Mock.Verify(Mock mock, LambdaExpression expression, Times times, String failMessage)
at Moq.Mock1.Verify(Expression1 expression, Times times, String failMessage)
at CtCore.Email.Test.Common.Utils.LoggerUtils.VerifyLog[T](Mock`1 loggerMock, LogLevel level, String message, Times times, String failMessage) in D:\ct.git\secure-document-vault\ctcore-email\CtCore.Email.Test.Common\Utils\LoggerUtils.cs:line 31

@aperisic

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@aperisic aperisic commented Mar 19, 2020

Didn't work for me

This worked for me. Notice that I decided to use Contains instead of equal but that should not affect the result. If something does not match starting from message text to signature it will say 0 occurences. I took me some time to find the solution.

         loggerMock.Verify(
            x => x.Log(
                level,
                It.IsAny<EventId>(),
                It.Is<It.IsAnyType>((o, t) => o.ToString().Contains(message)),
                It.IsAny<Exception>(),
                (Func<It.IsAnyType, Exception, string>) It.IsAny<object>()),
            times);
@WolfyUK

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@WolfyUK WolfyUK commented May 18, 2020

Thanks, @aperisic. Your solution works for .NET Core 3.1. The original solution worked for .NET Core 2.1 but failed after migration to v3.

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