function fizzBuzz(countTo) {
  var result = [];
  for (var i=1; i <= countTo; i++) {
    if (i % 15 === 0) {
      result.push('fizzbuzz');
    }
    else if (i % 5 === 0) {
      result.push('buzz');
    }
    else if (i % 3 === 0) {
      result.push('fizz');
    }
    else {
      result.push(i);
    }
  }
  return result;
}

// tests
(function testFizzBuzz() {
  // we'll use the variables in our test cases
  var countTo = 16;
  var expected = [
    1, 2, 'fizz', 4, 'buzz', 'fizz', 7, 8, 'fizz',
    'buzz', 11, 'fizz', 13, 14, 'fizzbuzz', 16
  ];

  var actual = fizzBuzz(countTo) || [];

  if (
    expected.length === actual.length &&
    expected.every(function(item, index) {
      return actual[index] === item;}) ) {

      console.log('SUCCESS: fizzBuzz is working');
  }
  else {
    console.log('FAILURE: fizzBuzz is not working');
  }
})();