unit test for the following code

Question

public static class myValidationExt
    {
public static IRuleBuilderOptions onlyPositive(this IRuleBuilder ruleBuilder)
            where TProperty : struct, IComparable, IComparable
        {
            return ruleBuilder.GreaterThan(default(TProperty)).WithMessage("StudentId should only be greater than zero");
        }
       }

[Test]
[ExpectedException(typeof(Exception), ExpectedMessage = "StudentId should only be greater than zero")]
 public void Positive_Valuelessthanzero_ValidationPassed()
 {
    //Arrange
    Thread.CurrentThread.CurrentCulture = new CultureInfo("en-us");

    //Act
    var myString = myValidationExt.onlyPositive(*******); // How to pass the parameter???

    //Assert

}