What is the legal test for a plaintiff to amend their complaint?

"To satisfy that burden on appeal, a plaintiff 'must show in what manner he can amend his complaint and how that amendment will change the legal effect of his pleading.' [Citation.] The assertion of an abstract right to amend does not satisfy this burden. [Citation.] Plaintiff must clearly and specifically set forth the 'applicable substantive law' [citation] and the legal basis for amendment, i.e., the elements of the cause of action and authority for it. Further, plaintiff must set forth factual allegations that sufficiently state all required elements of that cause of action. [Citations.] Allegations must be factual and specific, not vague or conclusionary. [Citation.]" (Rakestraw v. California Physicians' Service (2000) 81 Cal.App.4th 39, 43-44.)