old_contents: 'use strict';
  
  module.exports = function ($fs, matchers) {
    matchers = matchers.map(function (matcher) {
      return matcher($fs);
    });
  
    return function (file, code) {
      var matches = [];
  
      matchers.forEach(function (matcher) {
        matches = matches.concat(matcher(file, code));
      });
  
      return matches;
    };
  };
  
new_contents: 'use strict';
  
  module.exports = function ($fs, matchers) {
    matchers = matchers.map(function (matcher) {
      return matcher($fs);
    });
  
    return function (file, code) {
      return matchers.reduce(function (arr, matcher) {
        return arr.concat(matcher(file, code));
      }, []);
    };
  };
  
subject: Use reduce instead of forEach.