public function testPos()
{
$this->assertNull(StringHelper::pos(null, 'sad'));
$this->assertNull(StringHelper::pos('a', 'sad', 10));
$this->assertEquals(1, StringHelper::pos('lakanahbaha', 'a'));
$this->assertEquals(10, StringHelper::pos('lakanahbahakjlapaosa', 'a', 5));
$this->assertEquals(19, StringHelper::pos('lakanahbahakjlapaosa', 'a', -1));
$this->assertEquals(16, StringHelper::pos('lakanahbahakjlapaosa', 'a', -2));
}
