public void FilterTest()
{
// Given
var a = new[] { null, "", "David", "Hong" };
// When we collect non-null/empty strings
var b = a.Filter(x => !string.IsNullOrEmpty(x));
// Then
Assert.AreEqual(4, a.Length);
Assert.AreEqual(2, b.Length);
Assert.AreEqual("David", b[0]);
}