unit test for the following code

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
}