Codility demo test (PHP)

## codility_demo_test.php
<?php
function equi($A) {
  $lower_elements_sum = 0;
  $higher_elements_sum = array_sum($A);

  for ($i = 0, $cnt = count($A); $i < $cnt; $i++) {
    if (isset($A[$i - 1])) {
      $lower_elements_sum += $A[$i - 1];
    }
    $higher_elements_sum -= $A[$i];

    if ($lower_elements_sum == $higher_elements_sum) {
      return $i;
    }
  }

  return -1;
}

class EquiTest extends PHPUnit_Framework_TestCase {

  /**
   * @dataProvider provider
   */
  public function testEqui($A, $acceptable_results) {
    $this->assertTrue(in_array(equi($A), $acceptable_results));
  }

  public function provider() {
    return array(
      array(array(-7, 1, 5, 2, -4, 3, 0), array(3, 6)),
      array(array(3, 2, 1, -6, 0), array(4)),
      array(array(0, 3, 2, 1, -6), array(0)),
      array(array(1, 2, 3, 4, 5, 6), array(-1))
    );
  }
}