What is the test for review of an extraordinary writ?

determining the propriety of an extraordinary writ include that the issue tendered presents a significant and novel constitutional issue, or the party seeking the writ lacks an adequate means by which to attain relief], citing Britt v. Superior Court (1978) 20 Cal.3d 844, 851-852, 143 Cal.Rptr. 695, 574 P.2d 766 [discovery order compelling disclosure of information as to plaintiffs' and nonparties' private associational activities raised significant and novel constitutional issues of great importance, justifying review by extraordinary writ].)