public function testSubstring()
{
$this->eq(s::substring('abcdef', 2, 3), 'cde');
$this->eq(s::substring('abcdef', 2), 'cdef');
$this->eq(s::substring('abcdef', 2, 1000), 'cdef');
$this->eq(s::substring('abcdef', 1000), '');
$this->eq(s::substring('abcdef', 1000, 3), '');
$this->eq(s::substring('abcdef', 2, 0), '');
$this->eq(s::substring('abcdef', -2), 'ef');
$this->eq(s::substring('abcdef', -4, 2), 'cd');
$this->eq(s::substring('abcdef', -1000), 'abcdef');
$this->eq(s::substring('abcdef', -7, 3), 'ab');
$this->eq(s::substring('', 2, 4), '');
}
public function substring($offset, $length = null)
{
return new self(s::substring($this->value, $offset, $length));
}