Get mocha test keywords to show in Emacs imenu

mocha.el

(defun js2-imenu-make-index ()
  (save-excursion
    (imenu--generic-function '(("describe" "\\s-*describe\\s-*([\"']\\(.+\\)[\"']\\s-*,.*" 1)
                               ("it" "\\s-*it\\s-*([\"']\\(.+\\)[\"']\\s-*,.*" 1)
                               ("before" "\\s-*before\\s-*([\"']\\(.+\\)[\"']\\s-*,.*" 1)
                               ("after" "\\s-*after\\s-*([\"']\\(.+\\)[\"']\\s-*,.*" 1)

                               ;;add more keyword for mocha here
                               ("Function" "function[ \t]+\\([a-zA-Z0-9_$.]+\\)[ \t]*(" 1)
                               ("Function" "^[ \t]*\\([a-zA-Z0-9_$.]+\\)[ \t]*=[ \t]*function[ \t]*(" 1)))))

(add-hook 'js2-mode-hook
          (lambda ()
            (setq imenu-create-index-function 'js2-imenu-make-index)))