read the assertion message, not the line of code:

Invalid result for s = "", part1 = "ac", part2 = "ab"
Expected: false
Actual: true

why the test do_test("", "ac", "ab", false) return false :) isn't the part1 contain "" in its?

God i love haskell

when you want to solve a problem, better way is using the fundamentals of the language not the built-in function.

generic, works for lists and for strings (and probably iterables in general)

That rocks. The lookahead and keeping matches techniques are essentials.

Classes are just syntactic sugar meant to encapsulate code and abstract(hiding unnecessary details) code. The code would still work in this case without classes and by simply just writing the function

I definitely prefer readability, lol. I remember when I was starting out and hooked on code golf.

Nice parser

/1 refers to the first matching group in regexp (so literally the pattern is that the same letter should occur twice in a row)

Yes Of Course it can simply work without classes. Just write the function outside of the class code block literal and invoke the function like this: findSmallestInt([23, 45, 67])

it's not a completely ridiculous solution though.

What is your point exactly, did the chicken lay an egg or the egg produce a chicken?