This would solve issues with empties created from splits on pesky spaces, but doesn't handle the scenario where the string ONLY contains a space (which isn't eleminated as a possibility in the brief), which would result in Min failing due to no elements in the sequence.

Assert.AreEqual(0, Kata.FindShort(" "));

This solution is clean and simple, but doesn't take into account if the string, while not empty, contains any number of whitespace that aren't perfectly placed in the string (i.e. whitespace in the beginning or end or double-spaced).

Assert.AreEqual(1, Kata.FindShort(" a"));
Assert.AreEqual(1, Kata.FindShort("a "));
Assert.AreEqual(2, Kata.FindShort("an amp"));