fix: add testcast for PutInteger

[atgane]

I've implemented three parts to catch errors.

1. Receive an error if the len(data) is less than integer.size.
2. if integer.Encoding is not signed, throw error if it exceeds the maximum value of the unsigned size.
3. if integer.Encoding is signed, throw error when n is in a range that cannot be converted from uint64.

For example, the red part below throws an error.

Fixes #1208

[ti-mo]

Nit: technically, data is a byte slice, not an array. Also, it's always better to tell the user what the problem is. Sure the byte slice is smaller, but why is that an issue?

Suggested change

	return fmt.Errorf("byte array size %d is less than the integer size %d", len(data), integer.Size)
	return fmt.Errorf("can't fit an integer of size %d into a byte slice of length %d", integer.Size, len(data))

[ti-mo]

This is hard to read. Try:

Suggested change

	if !(n <= upperBound || lowerBound < n) {
	if n > upperBound || n < lowerBound {

[ti-mo]

Why is this called lowerBound if the value used is math.MaxUint64? Wouldn't this typically be used as an upper bound? Also, there's no need to perform this check on unsigned ints if we enforce some kind of minimum length of data.

[ti-mo]

Instead of the upperBound/lowerBound stuff from above, what about something like:

Suggested change

	case 1:
	case 1:
	if integer.Encoding == btf.Signed && (n > math.MaxInt8 || n < math.MinInt8) {
	return fmt.Errorf("...")
	}

This makes it stupidly obvious what the intention is and avoids the subtle math. Go defines all these constants, so we should just make use of them.

[atgane]

That looks good, but math.MinInt8 is not unsigned value, so condition can be

(n > math.MaxInt8 && n < math.MaxUint64 - math.MaxInt8)

And I'll change to return the error message only if it's signed conditions.