Wrapper class to disable debug assert ui from popping up in unit tests. (I know it should not be needed, but you know how it goes.)

DebugAssertDialogDisabler.cs

using System;
using System.Diagnostics;
using System.Linq;

public class DebugAssertDialogDisabler : IDisposable
{
    private readonly DefaultTraceListener _alteredListener;
        
    public DebugAssertDialogDisabler()
    {
        foreach (var tempListener in Debug.Listeners.OfType<DefaultTraceListener>())
        {
            if (tempListener.AssertUiEnabled)
            {
                _alteredListener = tempListener;
                tempListener.AssertUiEnabled = false;
            }

            return;
        }
    }

    public void Dispose()
    {
        if (null != _alteredListener)
        {
            _alteredListener.AssertUiEnabled = true;
        }
    }
}

DebugAssertDialogDisablerExample.cs

using System;
using System.Diagnostics;
using NUnit.Framework;

public class ExampleTests
{
    private void SirAssertsALot()
    {
        Debug.Fail("kaboom");
    }

    [Test]
    public void DebugAssertDialogShouldNotPop()
    {
        // arrange
        using (new DebugAssertDialogDisabler())
        {
            // act
            SirAssertsALot();

            // assert
            Assert.That(true, Is.Not.False);
        }
    }
}