public function get_types_by_extension_test()
 {
     $this->assert_equal("image/jpeg", legal_file::get_types_by_extension("jpg"));
     // photo
     $this->assert_equal("video/x-flv", legal_file::get_types_by_extension("FLV"));
     // movie
     $this->assert_equal(null, legal_file::get_types_by_extension("php"));
     // invalid
     $this->assert_equal(null, legal_file::get_types_by_extension("php.flv"));
     // invalid w/ .
     // No extension returns full array
     $this->assert_equal(9, count(legal_file::get_types_by_extension()));
 }