Perhaps include a fail test for -Infinity

Hm, I'm not sure that JavaScript Infinity will convert to C++ properly here.

OK, so JavaScript Infinity translates to std::numeric_limits<double>::infinity() in C++. So, I changed max_buffer_ to a double.

Error message needs to be updated to reflect the new constraint (It now accepts any positive number, not just unsigned integer).

That's a good point. The integer check is still required otherwise we'll have nonsense things like 0.1 accepted as the maxBuffer. The check should likely be something like:

if ((Number.isInteger(options.maxBuffer) || options.maxBuffer === Infinity) &&
    options.maxBuffer >= 0) {
  ...
}

And the error message should certainly be updated but that would upgrade this to a semver-major change

0.1 is technically fine as a maxBuffer value, even if it is a bit weird. We're just going to be doing comparisons against the value to see if we surpass it.

And the error message should certainly be updated but that would upgrade this to a semver-major change

This builds on an existing semver major change, so this is going to be semver major regardless.

That's a good point. The integer check is still required otherwise we'll have nonsense things like 0.1 accepted as the maxBuffer. The check should likely be something like:

if ((Number.isInteger(options.maxBuffer) || options.maxBuffer === Infinity) &&
    options.maxBuffer >= 0) {
  ...
}

And the error message should certainly be updated but that would upgrade this to a semver-major change