What is the test for the right of a single person to cast their ballot at the same time as a second person?

"[E]ach and every citizen has an inalienable right to full and effective participation in the political process[ ] ...." Reynolds v. Sims , 377 U.S. 533, 565, 84 S.Ct. 1362, 12 L.Ed.2d 506 (1964). That includes the right to "cast [one's] votes effectively," which requires that no voter be "denied an opportunity to cast a ballot at the same time and with the same degree of choice among candidates available to other voters." Dudum v. Arntz , 640 F.3d 1098, 1106, 1109 (9th Cir. 2011) (citation omitted).