What is the test for a motion to amend the pleadings in a personal injury case?

"Motions for leave to amend are directed to the sound discretion of the judge: 'The court may, in furtherance of justice and on any terms as may be proper, allow a party to amend any pleading. . . .' (Code Civ. Proc., 473, subd. (a)(1).) However, the court's discretion will usually be exercised liberally to permit amendment of the pleadings. The policy favoring amendment is so strong that it is a rare case in which denial of leave to amend can be justified. 'Leave to amend should be denied only where the facts are not in dispute, and the nature of the plaintiff's claim is clear, but under substantive law, no liability exists and no amendment would change the result.'" (Citations omitted.) (Howard v. County of San Diego (2010) 184 Cal.App.4th 1422, 1428.)