public void TestLength()
{
var mem = new byte[100];
var ss = new SpanStream(mem);
Assert.Equal(100, ss.Length);
ss.SetLength(0);
Assert.Equal(0, ss.Length);
Assert.Equal(100, ss.MaxLength);
ss.Write((UInt32)0);
Assert.Equal(4, ss.Length);
ss.Clear();
Assert.Equal(0, ss.Length);
}