public function test_parse_canvas_string_to_array()
 {
     $c = new canvas();
     $this->assertFalse($c->parse_canvas_string_to_array());
     $this->assertFalse($c->parse_canvas_string_to_array('aaaa'));
     $this->assertTrue($c->parse_canvas_string_to_array('aaaa<br />aaaa'));
     $c2 = new canvas(4, 4);
     $canvas_string = $c2->get_canvas_string();
     $c3 = new canvas(4, 4);
     $this->assertTrue($c3->parse_canvas_string_to_array($canvas_string));
 }