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Simplest way to calculate leap year

During my previous talk on C# programming, I have asked 'How to calculate a leap and what is the easiest way to make it testable.
 
There're numerous answers from the audience. I was surprised that everyone is doing all the old way. In following code snippet, I found this is the easiest and shortest one way:
 
  1. public static bool IsLeapYear(int year)  
  2.        {  
  3.            return (year%4==0 || year%400==0);  
  4.        }  
Above, method is just asking to supply an integer having year and it will return true/false quoting whether the year is a leap year. The idea behind this is the common i.e. a leap year which comes at every fourth year.
  1. [TestFixture]  
  2.     [Category("The LeapYear")]  
  3.     public class LeapYearTest  
  4.     {  
  5.         [Test]  
  6.         public void CanTestForLeapYear()  
  7.         {  
  8.             Assert.That(true, Is.EqualTo(LeapYear.IsLeapYear(1996)));  
  9.         }  
  10.   
  11.         [Test]  
  12.         [TestCase(false, 2013)]  
  13.         [TestCase(false, 2001)]  
  14.         [TestCase(true, 1996)]  
  15.         [TestCase(true, 1992)]  
  16.         public void CanTestForLeapYears(bool expectedResult, int year)  
  17.         {  
  18.             Assert.That(expectedResult, Is.EqualTo(LeapYear.IsLeapYear(year)));  
  19.         }  
  20.     }  
Above is showing Test, I did not make any special validation as this is just to say the shortest/easiest method to calculate leap year.
 
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