public void TestClientIdField()
{
Span <byte> expectedAsHex = stackalloc byte[] { 0x21, 0x22, 0x23, 0x24 };
ClientId expected = ClientId.ReadFrom(expectedAsHex);
Assert.Equal(expected, ClientServerMessage.GetClientId(_bytes));
Assert.Throws <ArgumentException>(() => ClientServerMessage.GetClientId(new Span <byte>(_bytes, 0, 11)));
}