DataAnnotations中必需的属性似乎不起作用

我创建了一个DataAnnotationValidator。我正在尝试用一个必需的字段属性测试它,当我的属性为null时,我不能让IsValid属性失败。当我使用指定范围之外的Range属性创建一个数字时,它确实可以正常工作。

public class TestEntityWithDataAnnotations
{
    public Guid Id { get; set; }

    [Required(ErrorMessage = "Required")]
    public string Name { get; set; }
}

[TestFixture]
public class DataAnnotationValidatorTest
{
    [Test]
    public void Validate_ReturnsFailure_WhenPropertyValidationIsNotValid()
    {
        var validator = new DataAnnotationValidator();
        var invalidEntity = new TestEntityWithDataAnnotations
        {
            Id = Guid.NewGuid()
        };
        var validationResult = validator.Validate(invalidEntity);

        Assert.IsFalse(validationResult.IsValid);
    }
}

public class DataAnnotationValidator
{
    public ValidationResult Validate(object obj)
    {
        Type objType = obj.GetType();            
        var typeDescriptor = GetTypeDescriptor(obj, objType);
        var validationResult = new ValidationResult();

        var classValidationResult = CheckClassIsValid(obj, typeDescriptor);
        if (!classValidationResult.IsValid)
        {
            validationResult.AddErrors(classValidationResult.Errors);
        }
        foreach (PropertyDescriptor propertyDescriptor in typeDescriptor.GetProperties())
        {
            // Loop over all of the properties on our object that have Validation Attributes
            var propValidationResult = CheckPropertyIsValid(obj, propertyDescriptor);
            if(!propValidationResult.IsValid)
            {
                validationResult.AddErrors(propValidationResult.Errors);
            }
        }
        return validationResult;
    }

    /// <summary>
    /// Checks to see if there are any class level validation attributes and runs them
    /// </summary>
    /// <returns></returns>
    private static ValidationResult CheckClassIsValid(object obj, ICustomTypeDescriptor typeDescriptor)
    {
        var errors = typeDescriptor.GetAttributes().OfType<ValidationAttribute>()
            .Where(x => !x.IsValid(obj))
            .Select(x => new ValidationError(typeDescriptor.GetClassName(), x.ErrorMessage));
        return new ValidationResult(errors.ToList());
    }

    /// <summary>
    /// Checks to see if a property has any DataAnnotations that it has violated
    /// </summary>
    private static ValidationResult CheckPropertyIsValid(object obj, PropertyDescriptor propertyDescriptor)
    {
        var errors = propertyDescriptor.Attributes.OfType<ValidationAttribute>()
            .Where(x => !x.IsValid(obj))
            .Select(x => new ValidationError(propertyDescriptor.Name, x.ErrorMessage));
        return new ValidationResult(errors.ToList());
    }

    /// <summary>
    /// Gets the model's type descriptor. In order to support the buddy class metadata model
    /// for LINQ to SQL and Entity Framework, it uses
    /// <see cref="AssociatedMetadataTypeTypeDescriptionProvider"/>.
    /// </summary>
    /// <param name="obj">The model object</param>
    /// <param name="objType">The type of the model object</param>
    /// <returns>The model's type descriptor</returns>
    private static ICustomTypeDescriptor GetTypeDescriptor(object obj, Type objType)
    {
        var provider = new AssociatedMetadataTypeTypeDescriptionProvider(objType);
        return provider.GetTypeDescriptor(objType, obj);
    }
}