我正在对带有日期的请求进行单元测试。这些日期带有相同的时间戳，并且测试失败。在不同的时间戳下，测试运行良好，但是在相同的时间戳下，测试返回错误结果。

测试代码：

[Fact]
public void ShouldHaveValidationSuccessWhenStartDateIsLessOrEqualToFinishDate()
{
    //Arrange
    var request = new RegisterRequest { FinishDate = DateTimeOffset.UtcNow,StartDate = DateTimeOffset.UtcNow };
    var sut = new RegisterRequestValidator();

    //act
    var result = sut.TestValidate(request);

    //Assert
    result.ShouldNotHaveValidationErrorFor(x => x.StartDate);
}

验证者代码：

public RegisterRequestValidator()
{
    RuleFor(req => req.StartDate).LessThanOrEqualTo(req => req.FinishDate).When(HasStartDate);
}

protected bool HasStartDate(RegisterRequest req) => req.StartDate != null;

RegisterRequest代码：

public sealed class RegisterRequest : IRequest<OperationResult<IQueryable<EntityViewModel>>>
{
    public DateTimeOffset? StartDate { get; set; }
    public DateTimeOffset? FinishDate { get; set; }
}

我得到的错误是

Message: 
    FluentValidation.TestHelper.ValidationTestException : Expected no validation errors for property StartDate
    ----
    Validation Errors:
    [0]: 'Start Date' must be less than or equal to '07/11/2019 12:50:58 +00:00'.

为什么会这样？