Set custom value for init-only properties on AutoFixture

AutoFixtureExtensions.cs

using System.Linq.Expressions;
using AutoFixture;

public static class AutoFixtureExtensions
{
    public static FixtureCustomization<T> For<T>(this Fixture fixture) => new(fixture);

    public class FixtureCustomization<T>(Fixture fixture)
    {
        public FixtureCustomization<T> With<TProp>(Expression<Func<T, TProp>> expr, TProp value)
        {
            fixture.Customizations.Add(new OverridePropertyBuilder<T, TProp>(expr, value));
            return this;
        }

        public T Create() => fixture.Create<T>();
    }
}

OverridePropertyBuilder.cs

using System.Linq.Expressions;
using System.Reflection;
using AutoFixture.Kernel;

public class OverridePropertyBuilder<T, TProp>(Expression<Func<T, TProp>> expr, TProp value) : ISpecimenBuilder
{
    private readonly PropertyInfo _propertyInfo =
        (expr.Body as MemberExpression)?.Member as PropertyInfo
        ?? throw new InvalidOperationException("invalid property expression");

    public object? Create(object request, ISpecimenContext context)
    {
        return
            request is ParameterInfo pi
            && pi.ParameterType == typeof(TProp)
            && string.Equals(pi.Name, _propertyInfo.Name, StringComparison.OrdinalIgnoreCase)
            ? value
            : new NoSpecimen();
    }
}