assertassert is an alias for `cl-assert' in `
cl.el'. (assert FORM &optional SHOW-ARGS STRING &rest ARGS) Verify that FORM returns non-nil; signal an error if not. Second arg SHOW-ARGS means to include arguments of FORM in message. Other args STRING and ARGS... are arguments to be passed to `error'. They are not evaluated unless the assertion fails. If STRING is omitted, a default message listing FORM itself is used.