All characters considered as vowel are currently listed in the description (y/Y are not listed as vowels)

Hours later; I added fixed test that your first (?) solution doesn't pass anymore. Thanks for your post.

There is a small flaw (or typo) in your code; the 200 random tests don't catch it every time so yes by mashing the submit button it happens you pass. When your code fails it is with long arrays of long strings and I can't put these long tests in fixed tests; until now I was not able to reproduce the same things with a short test. Sorry...

Please look at the first rule again.

I tried to debug your code. In the first fixed test of "Sample Tests", I got:

Fixed_Tests
 Log
Actual: {103, 101}
Error testing StepInPrimes::step(2, 100, 110)!
Expected: {101, 103}
Actual: {103, 101}

or for another one:

Fixed_Tests
 Log
Actual: {5, 3}
Error testing StepInPrimes::step(2, 2, 50)!
Expected: {3, 5}
Actual: {5, 3}

It seems (at least...) that your return is always in wrong order... Try first to correct that.

Sorry about that, the testing framework doesn't know how to print pairs so when the solution fails it reports " [unsupported type]". This issue was already showing (maybe you can see it some posts below). The only way is to have a code that doesnt't fail:-(
Maybe you could print yourself the input and your output. Example for output:

std::string output_pair(std::pair<long long, long long> p) {
  return "{" + to_string(p.first) + ", " + to_string(p.second) + "}";
}

Hope that helps!