FakeLoggingExtensionGenerator.md

Fake Logging Extension Generator

When your test project references Microsoft.Extensions.Diagnostics.Testing, this generator creates an AddFakeLogging() extension method that sets up fake logging for testing.

Features

• Automatically generates when Microsoft.Extensions.Diagnostics.Testing is referenced
• Provides access to logged messages for verification
• Uses Microsoft's official testing helpers

Installation

Install the Microsoft.Extensions.Diagnostics.Testing package:

dotnet add package Microsoft.Extensions.Diagnostics.Testing

Usage

using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Logging.Testing;

public class MyService
{
    private readonly ILogger<MyService> _logger;
    
    public MyService(ILogger<MyService> logger)
    {
        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
    }
    
    public void DoWork()
    {
        _logger.LogInformation("Starting work");
        _logger.LogDebug("Debug message");
        _logger.LogWarning("Warning message");
    }
}

[TestClass]
public class MyServiceTests
{
    [TestMethod]
    public void Test_WithFakeLogging()
    {
        AutoMocker mocker = new();
        
        // Use the generated AddFakeLogging extension method
        mocker.AddFakeLogging();
        var provider = mocker.Get<FakeLoggerProvider>();

        MyService service = mocker.CreateInstance<MyService>();
        service.DoWork();

        // Verify logged messages
        var logs = provider.Collector.GetSnapshot();
        Assert.IsTrue(logs.Any(log => log.Message == "Starting work"));
        Assert.IsTrue(logs.Any(log => log.Message == "Debug message"));
        Assert.IsTrue(logs.Any(log => log.Message == "Warning message"));
    }
}

Generated Extension Method

The generator creates:

public static AutoMocker AddFakeLogging(this AutoMocker mocker)
{
    // Sets up FakeLoggerProvider for capturing log messages
    // Configures AutoMocker to use fake loggers
}

How It Works

The AddFakeLogging() method:

1. Creates a FakeLoggerProvider instance
2. Registers a custom FakeLoggerResolver with the AutoMocker
3. Inserts the resolver after the CacheResolver in the resolver chain
4. This ensures all ILogger<T> instances use the fake logger infrastructure

The FakeLoggerProvider captures all log messages, allowing you to:

• Verify that specific messages were logged
• Check log levels
• Inspect logged data and state
• Validate logging behavior in your tests

Advanced Usage

Testing Different Log Levels

[TestMethod]
public void Test_LogLevels()
{
    AutoMocker mocker = new();
    mocker.AddFakeLogging();
    var provider = mocker.Get<FakeLoggerProvider>();

    MyService service = mocker.CreateInstance<MyService>();
    service.DoWork();

    var logs = provider.Collector.GetSnapshot();
    
    // Check for specific log levels
    Assert.IsTrue(logs.Any(log => log.Level == LogLevel.Information));
    Assert.IsTrue(logs.Any(log => log.Level == LogLevel.Debug));
    Assert.IsTrue(logs.Any(log => log.Level == LogLevel.Warning));
}

Accessing ILoggerFactory

[TestMethod]
public void Test_LoggerFactory()
{
    AutoMocker mocker = new();
    mocker.AddFakeLogging();

    // ILoggerFactory is also available
    var factory = mocker.Get<ILoggerFactory>();
    var logger = factory.CreateLogger("CustomCategory");
    
    logger.LogInformation("Test message");
    
    var provider = mocker.Get<FakeLoggerProvider>();
    var logs = provider.Collector.GetSnapshot();
    Assert.IsTrue(logs.Any(log => log.Message == "Test message"));
}

Disabling the Generator

You can disable this generator using an MSBuild property in your test project's .csproj file:

<PropertyGroup>
  <EnableMoqAutoMockerFakeLoggingGenerator>false</EnableMoqAutoMockerFakeLoggingGenerator>
</PropertyGroup>

Example: Disabling in Project File

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>net8.0</TargetFramework>
    
    <!-- Disable Fake Logging Extension Generator -->
    <EnableMoqAutoMockerFakeLoggingGenerator>false</EnableMoqAutoMockerFakeLoggingGenerator>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Moq.AutoMock" Version="3.5.0" />
    <PackageReference Include="Microsoft.Extensions.Diagnostics.Testing" Version="8.0.0" />
  </ItemGroup>
</Project>

Troubleshooting

Extension Method Not Available

1. Verify Microsoft.Extensions.Diagnostics.Testing is referenced in your test project
2. Check that the generator is not disabled in your .csproj
3. Rebuild the project to trigger generator execution
4. Ensure you're using the Moq.AutoMock namespace

Logs Not Being Captured

1. Make sure you're calling AddFakeLogging() before creating your instance
2. Verify you're getting the FakeLoggerProvider from the same AutoMocker instance
3. Check that your service is actually using the injected logger