What is the test for equitable tolling in a habeas petition?

[1] Rivera argues that the district court erred by denying his motion to equitably toll the one-year limitations period for filing his habeas petition. See 28 U.S.C. 2255(f)(1). We review the district court's legal conclusions de novo and its factual findings for clear error. Jenkins v. Greene, 630 F.3d 298, 302 (2d Cir. 2010). Where a district court declines to grant equitable tolling "in the exercise of its discretion, we apply an abuse of discretion standard." Id.