What is the test for a motion to amend a pleading to amend the pleading?

" ' "[T]he trial court has wide discretion in allowing the amendment of any pleading [citations], [and] as a matter of policy the ruling of the trial court in such matters will be upheld unless a manifest or gross abuse of discretion is shown. [Citations.]" ' [Citations.] Courts must apply a policy of great liberality in permitting amendments to the complaint at any stage of the proceedings, up to and including trial, when no prejudice is shown to the adverse party. [Citation.] However, ' "even if a good amendment is proposed in proper form, unwarranted delay in presenting it mayof itselfbe a valid reason for denial." ' " (Huff v. Wilkins (2006) 138 Cal.App.4th 732, 746 (Huff).)