What is the test for a motion to set aside a default judgment?

The law favors trial on the merits; therefore, we liberally construe motions to set aside default judgments in favor of the party seeking relief. (Shamblin v. Brattain (1988) 44 Cal.3d 474, 478.) Code of Civil Procedure section 473 (section 473) provides for both discretionary and mandatory relief. If an attorney's admitted neglect causes entry of a default judgment, relief is mandatory: "[T]he court shall, whenever an application for relief is made no more than six months after entry of judgment, is in proper form, and is accompanied by an attorney's sworn affidavit attesting to his or her mistake, inadvertence, surprise, or neglect, vacate any (1) resulting default entered by the clerk against his or her client, and which will result in entry of a default judgment, or (2) resulting default judgment or dismissal entered against his or her client, unless the court finds that the default or dismissal was not in fact caused by the attorney's mistake, inadvertence, surprise, or neglect." ( 473, subd. (b).)