using FluentValidation;

using System;

public class Program

{

    public static void Main()

    {

        Test test = new();

        TestValidator validator = new();

        var validationResults = validator.Validate(test);

        foreach(var vr in validationResults.Errors)

        {

            Console.WriteLine($"{vr.PropertyName} {vr.ErrorMessage}");

        }

    }

}

​

public class Test

{

    public bool? A { get; set; }

    public bool? B { get; set; } = true;

    public bool? C { get; set; } = false;

    public bool D { get; set; } = false;

    public bool E { get; set; } = true;

}

​

public class TestValidator : AbstractValidator<Test>

{

    public TestValidator()

    {

        RuleFor(x => x.A).NotEmpty();

        RuleFor(x => x.B).NotEmpty();

        RuleFor(x => x.C).NotEmpty();

        RuleFor(x => x.D).NotEmpty();

        RuleFor(x => x.E).NotEmpty();

    }

}