From rombert's comment on the pull request:

Some basic tests are quite easy to add, e.g.

public function testSpecialSplit() {

    self::assertEquals(array('a', ' b'), special_split('a, b'));
}

public function testProcessSpecialValues() {

    self::assertEquals(array(1,2,3), process_complex_value('array(1, 2, 3)'));
    self::assertEquals(array(1,2,3), process_complex_value('array(1, 2, 3);'));
}

public function testConstantReplace() {

    self::assertEquals(ON, constant_replace('ON'));
    self::assertEquals('NotAConstant', constant_replace('NotAConstant'));
}

Of course, there's much more to test