public void List_DefaultIfEmpty()
{
var list = ReadOnlyList.DefaultIfEmpty(new int[0], 999);
Assert.AreEqual(1, list.Count);
Assert.AreEqual(999, list[0]);
list = ReadOnlyList.DefaultIfEmpty(new int[] { 9, 3, 1 }, 999);
Assert.AreEqual(3, list.Count);
Assert.AreEqual(9, list[0]);
Assert.AreEqual(3, list[1]);
Assert.AreEqual(1, list[2]);
var list2 = ReadOnlyList.DefaultIfEmpty(new string[0], "999");
Assert.AreEqual(1, list2.Count);
Assert.AreEqual("999", list2[0]);
list2 = ReadOnlyList.DefaultIfEmpty(new string[] { "three", "two", "one" }, "999");
Assert.AreEqual(3, list2.Count);
Assert.AreEqual("three", list2[0]);
Assert.AreEqual("two", list2[1]);
Assert.AreEqual("one", list2[2]);
}