https://exercism.io/tracks/csharp/exercises/leap/solutions/a84d2311891b4c4db01bb14dde3e5231

Leap.cs

using System;

public static class Leap
{
    public static bool IsLeapYear(int year)
    {
        bool multipleOf4 = YearIsDivisibleByFactor(year, 4);
        bool multipleOf100 = YearIsDivisibleByFactor(year, 100);
        bool multipleOf400 = YearIsDivisibleByFactor(year, 400);

        return !multipleOf4 ? false : !(multipleOf4 && (multipleOf100 && !multipleOf400));
    }

    public static bool YearIsDivisibleByFactor(int year, int divisor)
    {
        return (year % divisor) == 0;
    }
}

LeapTest.cs

// This file was auto-generated based on version 1.3.0 of the canonical data.

using Xunit;

public class LeapTest
{
    [Fact]
    public void Year_not_divisible_by_4_is_common_year()
    {
        Assert.False(Leap.IsLeapYear(2015));
    }

    [Fact]
    public void Year_divisible_by_4_not_divisible_by_100_is_leap_year()
    {
        Assert.True(Leap.IsLeapYear(1996));
    }

    [Fact]
    public void Year_divisible_by_100_not_divisible_by_400_is_common_year()
    {
        Assert.False(Leap.IsLeapYear(2100));
    }

    [Fact]
    public void Year_divisible_by_400_is_leap_year()
    {
        Assert.True(Leap.IsLeapYear(2000));
    }
}