How to mock ILogger.LogXXX methods on netcore 3.0

Question

Until now, we I was mocking the ILogger.LogXXX calls by following this approach.

Unfortunately, after updating the project to .net core 3.0, and if you're using strict mocks (Moq), it will always complain about not having a corresponding setup:

Moq.MockException : ILogger.Log<FormattedLogValues>(LogLevel.Information, 0, 
           Inicio de cancelamento de reserva:  Grm.GestaoFrotas.Dtos.Reservas.Mensagens.MsgCancelamentoReserva, 
           null, 
           Func<FormattedLogValues, Exception, string>) invocation failed with mock behavior Strict.
All invocations on the mock must have a corresponding setup.

Unfortunately, I can't simple change object with FormattedLogValues like this:

_container.GetMock<ILogger<GestorReservas>>()
          .Setup(l => l.Log(It.IsAny<LogLevel>(),
                            It.IsAny<EventId>(),
                            It.IsAny<FormattedLogValues>(),
                            It.IsAny<Exception>(),
                            It.IsAny<Func<FormattedLogValues, Exception, string>()));

This won't work because FormattedLogValues is internal.

I can always change the mocking strategy (strict to loose), but I'd prefer to keep it as it is (strict). So, any clues on how to solve this?

Thanks.

@Johnny could you post an example? I had the same issue, tried replacing `FormattedLogValues` with `It.IsAnyAtype` and now I'm getting another error: — Leandro López, Oct 28 '19 at 19:12
https://github.com/Moq/moq4/wiki/Quickstart, find matching generic type arguments... — Johnny, Oct 28 '19 at 19:14

score 3 · Answer 1 · answered Nov 16 '19 at 11:40

3

Try this:

//    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.4.0" />
//    <PackageReference Include="Moq" Version="4.13.1" />

container.GetMock<ILogger<GestorReservas>>()
          .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>())));

https://www.bountysource.com/issues/79804378-cannot-verify-calls-to-ilogger-in-net-core-3-0-preview-8-generic-type-matcher-doesn-t-work-with-verify

answered Nov 16 '19 at 11:40

Mukmyash

41
2

Please give some explanation of your solution rather than only code. – hivert Nov 16 '19 at 12:07
This does in fact fix the issue, but how? The key part is casting Any – carlin.scott Dec 22 '20 at 23:13

granadaCoder · Answer 2 · 2021-10-21T16:55:56.343

This expands on Muk's answer.

My addition is "ILoggerFactory"..and how you "code up" the actually logging inside your real class.

First, unit test code:

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


    private Mock<ILoggerFactory> GetDefaultILoggerFactoryMock()
    {
        Mock<ILoggerFactory> returnMock = new Mock<ILoggerFactory>(MockBehavior.Loose);
        returnMock.Setup(x => x.CreateLogger(It.IsAny<string>())).Returns(
            () =>
                this.GetDefaultILoggerMock<MyConcreteClassThatUsesILoggerFactoryInItsConstructor>().Object);
        return returnMock;
    }

    private Mock<ILogger<T>> GetDefaultILoggerMock<T>()
    {
        Mock<ILogger<T>> returnMock = new Mock<ILogger<T>>(MockBehavior.Strict);
        returnMock.Setup(
            m => m.Log(
                It.IsAny<LogLevel>(),
                It.IsAny<EventId>(),
                It.IsAny<object>(),
                It.IsAny<Exception>(),
                It.IsAny<Func<object, Exception, string>>())).Callback(
            (LogLevel ll, EventId eid, object obj1, Exception ex, Func<object, Exception, string> func) =>
            {
                Console.WriteLine(func.Invoke(obj1, ex));
            }).Verifiable();
        returnMock.Setup(m => m.IsEnabled(It.IsAny<LogLevel>())).Returns(false);
        return returnMock;
    }

Now, in your actual class (here I call it 'MyConcreteClassThatUsesILoggerFactoryInItsConstructor')..you need to use the NON EXTENSION METHOD of making log calls. (All the helper methods like LogInformation are static extension methods overloads)

So like this:

            Func<object, Exception, string> logMsgFunc = (a, b) => "MyDebugMessageOne";
            this.logger.Log(LogLevel.Debug, ushort.MaxValue, null, null, logMsgFunc);

or for one that is an exception

        catch (Exception ex)
        {
            Func<object, Exception, string> logMsgFunc = (a, b) => "MyErrorContextMessageTwo";
            this.logger.Log(LogLevel.Error, ushort.MaxValue, null, ex, logMsgFunc);
        }

If you do both of those things, especially the second part, you can Mock the ILoggerFactory / ILogger

Here is the germane parts of the class/constructor:

using Microsoft.Extensions.Logging;

public class MyConcreteClassThatUsesILoggerFactoryInItsConstructor : IMyConcreteClassThatUsesILoggerFactoryInItsConstructor
{
    public const string ErrorMsgILoggerFactoryIsNull = "ILoggerFactory is null";

    private readonly ILogger<MyConcreteClassThatUsesILoggerFactoryInItsConstructor> logger;
    

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

        this.logger = loggerFactory.CreateLogger<MyConcreteClassThatUsesILoggerFactoryInItsConstructor>();

    }

    public void DoSomething()
    {

        Func<object, Exception, string> logMsgFunc = (a, b) => "DoSomething Started";
        this.logger.Log(LogLevel.Debug, ushort.MaxValue, null, null, logMsgFunc);

        int div = 0;

        try
        {
            int x = 1 / div;
        }
        catch (Exception ex)
        {
            Func<object, Exception, string> errorMsgFunc = (a, b) => string.Format("MyErrorContextMessageTwo (div='{0}')", div);
            this.logger.Log(LogLevel.Error, ushort.MaxValue, null, ex, errorMsgFunc);
        }


    }

}

How to mock ILogger.LogXXX methods on netcore 3.0

2 Answers2