code: function(dir, prefix) {
      if (fs.existsSync(dir)) {
        let dirname = path.relative(this.project.root, dir);
        let globs = this.parentRegistry.extensionsForType('js').map((extension) => `**/*.${extension}`);
  
        return walkSync(dir, { directories: false, globs }).map(file => {
          let module = prefix + '/' + file.replace(EXT_RE, '.js');
          this.fileLookup[module] = path.join(dirname, file);
          return module;
        });
      } else {
        return [];
      }
    }
docs: Get paths to include for coverage
  @param {String} dir Include all js files under this directory.
  @param {String} prefix The prefix to the ember module ('app', 'dummy' or the name of the addon).
  @returns {Array<String>} include paths