What is the test for a direct attack on a final judgment by way of an independent action to set it aside?

"A direct attack on an otherwise final, valid judgment by way of an independent action to set it aside [citations] is permitted where it appears that the complaining party was fraudulently prevented from presenting his claim or defense in the prior action." (Kachig v. Boothe (1971) 22 Cal.App.3d 626, 632, 99 Cal.Rptr. 393.) This is known as extrinsic fraud. The rule is premised on the "important public policy that litigants be afforded a fair adversary proceeding in which fully to present their case. [Citation.]" (Ibid.) An example of extrinsic fraud occurs when an unsuccessful party is kept from appearing in the action by a false promise of a compromise. ( Id. at p. 633, 99 Cal.Rptr. 393.)