void roundtrip(ulong x)
{
// Use some padding bytes to check nonzero offsets.
var pad = 5;
var buf = new byte[VarInt.MaxVarIntLen64 + pad];
int n = VarInt.PutUvarInt(buf, pad, x);
var ret = VarInt.UvarInt(buf, pad);
Assert.AreEqual(n, ret.VarIntLength);
Assert.AreEqual(x, ret.Value);
}