anchor.diff:    final options = parser.parse(args);
     if (options["help"]) {
       print("""
  -Usage: compare_results.dart [OPTION]... [BEFORE] [AFTER]
  +Usage: compare_results.dart [OPTION]... BEFORE AFTER [APPROVED]
   Compare the old and new test results and list tests that pass the filters.
  +Three-way compare with the approved results if provided.
   All tests are listed if no filters are given.
   
   The options are as follows:
  
positive.code:   }
  
    final parameters = options.rest;
    if (parameters.length != 2) {
      print("error: Expected two parameters (results before and results after)");
      exitCode = 2;
      return;
    }
  
negative.code:       negatable: false);
    parser.addFlag("passing",
        abbr: 'p', negatable: false, help: "Show passing tests.");
    parser.addFlag("unapproved",
        abbr: 'U', negatable: false, help: "Show unapproved tests.");
    parser.addFlag("unchanged",
        abbr: 'u',
        negatable: false,
  