code: function () {
          var ret = {},
              that = this;
          this.files().forEach(function (file) {
              ret[file] = that.fileCoverageFor(file);
          });
          return ret;
      }
docs: returns file coverage information for all files. This has the same format as
  any of the objects passed in to the `add` method. The number of keys in this
  object will be a superset of all keys found in the objects passed to `add()`
  @method getFinalCoverage
  @return {Object} the merged coverage information