public void GetHashCode_Colision()
{
var a = new CssPropertiesSet();
var b = new CssPropertiesSet();
var prop1 = new MockProp1();
var prop2 = new MockProp2();
a.Add(prop1);
a.Add(prop2);
b.Add(prop1);
b.Add(prop2);
Assert.AreEqual(a.GetHashCode(), b.GetHashCode());
}