France, March 23 -- Senegal votes on Sunday in a presidential election that is expected to be the most tightly contested in years. Before polls opened, a team of a thousand observers drawn from civil society was preparing to monitor the long-awaited vote.

In Dakar, Senegal's capital, a team of volunteers were stationed behind laptops, phones to their ears.

On the other end of the line were observers on the ground across Senegal, calling in in a rehearsal for Sunday's vote.

"We're looking at areas that don't have network coverage so that we can flag them up in the database, and see which observers are having trouble sending messages correctly," explainedKhadija Mohamed, supervisor of the simulation exercise.

On the day of the vote itse...