Is there way to see log messages generated in a unit test in .NET Core?

Question

I have a C# project in .NET Core with unit tests. In order to better examine the flow through the code during a test I would really like to see the output of the NLog messages that are built into the code base.

I am using XUnit and I know XUnit has moved away from Console messages because of parallel test execution. For what I want to accomplish using ITestOutputHelper won't be very helpful.

Is there a way to get NLog logging to be included in test output?

Answer 1

I use something like this:

namespace Tests.Builders
{
    internal static class Logging
    {
        public static ILogger DefaultLogger()
        {
            return NullLogger();
        }

        public static ILogger NullLogger()
        {
            return Substitute.For<ILogger>();
        }

        public static ILogger XUnitLogger(ITestOutputHelper testOutputHelper)
        {
            // Step 1. Create configuration object 
            var config = new LoggingConfiguration();

            // Step 2. Create targets and add them to the configuration 
            var consoleTarget = new XUnitTarget(testOutputHelper);
            config.AddTarget("xunit", consoleTarget);

            // Step 3. Set target properties 
            consoleTarget.Layout = @"${date:format=HH\:mm\:ss} ${logger} ${message}";

            // Step 4. Define rules
            var rule1 = new LoggingRule("*", LogLevel.Trace, consoleTarget);
            config.LoggingRules.Add(rule1);

            // Step 5. Activate the configuration
            LogManager.Configuration = config;

            return LogManager.GetLogger("");
        }
    }

    [Target("XUnit")]
    public sealed class XUnitTarget : TargetWithLayout
    {
        private readonly ITestOutputHelper _output;

        public XUnitTarget(ITestOutputHelper testOutputHelper)
        {
            _output = testOutputHelper;
        }

        protected override void Write(LogEventInfo logEvent)
        {
            string logMessage = this.Layout.Render(logEvent);

            _output.WriteLine(logMessage);
        }
    }
}

public class SomeTests
{
    private readonly ITestOutputHelper _output;

    public SomeTests(ITestOutputHelper output)
    {
        _output = output;
    }

    [Fact]
    public void Lets_see_some_output()
    {
        var foo = new Foo(Logging.XUnitLogger(_output));

        var result = foo.ExecuteSomething();

        Assert.Equal(true, result);
    }
}