Just do what is fast in your particular language. Order of elements within a combination by definition does not matter.

Which is entirely correct.

The negative number issue is now fixed.

There's still a tab issue I forgot to fix, and it's now fixed.

It's not giving neg numbers. Closed

This issue no longer appears. Closed

same =(

Yeah, I've got exactly the same problem.
This may be fixed by replacing tabs with spaces on line 7 on tests file

I've got exactly the same problem

The following warning prevents me from submitting my otherwise correct solution:

/tmp/haskell116114-18-mo7fqm.mrxlpx2yb9/Main.hs:7:1: Warning:
Tab character

The test case doesn't consider the list has repeated element.
Like this, combinations 2 [1,1,1,1,1].

QuickCheck tests should not give negative numbers for group size (e.g. combinations -2 [1, 2, 3, 4])

Tests expect [[]] when inputting 0, but expect [] when inputting negative values or values greater than the length of the list.

Yes fitness[i] is the fitness of chromosome[i].
It looks like you are doing this in Ruby. In that case you should use an integer instead of a binary string.
The description states: "What the test will do is generate a random binary string of 35 digits (a random Integer with 35 bits for Ruby)".
So in Ruby we use Integers instead of strings (since we have Integers of arbitrarily large size already).