Grains - Javascript - problem with the test answer? Other people also seem to be using a workaround to make answer match test

[beansprout]

I found that for the test

test('total', () => {
    expect(grains.total()).toBe('18446744073709551615');
  });

using big-integer.js gave me an answer of '18446744073709551616' no matter what I did. So I looked at other people's answers to figure out what I was doing wrong.

What I found was that other people were just subtracting 1 from the 'total' method in their answers using a variety of different fixes so I did the same. There was only one test involving the total method so all tests passed that way.

However, upon reflection, maybe the test should be fixed.

Here was my total method:

total() {
    let tot = bigInt(0);
    for (let i = 2; i < 65; i++) {
      tot = tot + parseInt(this.square(i))
      }
      return bigInt(tot).minus(1).toString();
    }

The .minus(1) in the second to last line was my "fix".

Or, if I really am supposed to get '18446744073709551615' what should I be doing instead?
My full answer is here: https://exercism.io/my/solutions/2261a8c46c844d43992a4ac2c7ba5e03

Originally posted by @beansprout in exercism/r#106 (comment)
(moved because I was in the wrong track. Oops!)

[iHiD]

Hello :)

I believe the test is correct.

If you do the sum manually, you'll see you end up at the correct solution.

1 + 2 + 4 + 8 + 16 + 32 + 64 + 128 + 256 + 512 + 1024 + 2048 + 4096 + 8192 + 16384 + 32768 + 65536 + 131072 + 262144 + 524288 + 1048576 + 2097152 + 4194304 + 8388608 + 16777216 + 33554432 + 67108864 + 134217728 + 268435456 + 536870912 + 1073741824 + 2147483648 + 4294967296 + 8589934592 + 17179869184 + 34359738368 + 68719476736 + 137438953472 + 274877906944 + 549755813888 + 1099511627776 + 2199023255552 + 4398046511104 + 8796093022208 + 17592186044416 + 35184372088832 + 70368744177664 + 140737488355328 + 281474976710656 + 562949953421312 + 1125899906842624 + 2251799813685248 + 4503599627370496 + 9007199254740992 + 18014398509481984 + 36028797018963968 + 72057594037927936 + 144115188075855872 + 288230376151711744 + 576460752303423488 + 1152921504606846976 + 2305843009213693952 + 4611686018427387904 + 9223372036854775808 
=> 18446744073709551615