What is the test for establishing a violation of a prisoner's right to access to the courts?

To establish a violation of the right of access to the courts a prisoner must allege facts sufficient to show that: (1) a nonfrivolous legal attack on his conviction, sentence, or conditions of confinement has been frustrated or impeded, and (2) he has suffered an actual injury as a result. See Lewis, 518 U.S. at 353-55; Christopher v. Harbury, 536 U.S. 403, 415 (2002) (to state an access to courts violation, plaintiff must describe the non-frivolous nature of the "underlying cause of action, whether anticipated or lost"). The prisoner must demonstrate that he has suffered or will imminently suffer actual injury. Lewis, 518 U.S. at 348.