Some math:
There are 88 entries in this list.
88 * 64 bits = 5,632 bits.
5,632 bits / 8 bits per byte = 704 Bytes.

Found what happened, nevermind.

This message:

Expected: equal to ""
Actual: "

means that a test expects an empty string, but your solution returned a string with some non-printable characters (possibly a '\0'). The message looks bad because it is truncated because it contains an unprintable character at the beginning.

You are right that the message is confusing, but your solution most probably has a bug. It's difficult to say without knowing your code tho.

So, I can't pass the fixed tests (and only the fixed tests, I passed on everything else) in the full suite. The only error I get is this:
Expected: equal to ""
Actual: "

Even after implementing this line right before returning:
res.erase(std::remove(res.begin(), res.end(), ' '), res.end());
which removes all spaces, I get the same error.

This is for C++, and I have no idea how I would end up with a singular double-quotation mark, as strings are represented with 2 double-quotation marks.

Vague error message, could not complete Kata.