emacs-lisp-mode-hook

emacs-lisp-mode-hook is a variable defined in `elisp-mode.el'.
Its value is

(ert--activate-font-lock-keywords)

Original value was

• This variable may be risky if used as a file-local variable.

Documentation:
Hook run after entering Emacs-Lisp mode.
No problems result if this variable is not bound.
`add-hook' automatically binds it. (This is true for all hook variables.)

You can customize this variable.