},
		{
			example: hex("1bffffffffffffffff"),
			reject:  "2^64-1 overflows int64 and falling back to float64 (as with JSON) loses distinction between float and integer",
		},
		{
			example: hex("c249010000000000000000"),
			reject:  "decoding tagged positive bigint value to interface{} can't reproduce this value without losing distinction between float and integer",
			fixme:   "decoding bigint to interface{} must not produce math/big.Int",

				assertOnError: assertNilError,
			},
		})

		group(t, "unsigned bignum", []test{
			{
				name:  "rejected",
				in:    hex("c249010000000000000000"), // 2(18446744073709551616)
				fixme: "decoding cbor data tagged with 2 produces big.Int instead of rejecting",
				assertOnError: func(t *testing.T, e error) {