public void GetPart()
{
var map = new DocumentMap<string>();
map.Add(5, "test");
var relativeRanges = map.GetRelativeRange(new Range(1, 7));
Assert.AreEqual(1, relativeRanges.Count);
Assert.AreEqual("test", relativeRanges[0].Source);
Assert.AreEqual(new Range(1,5), relativeRanges[0].Range);
}