Final answer:
The unknown outcome of the war that Lincoln was referring to was the future of the South and the process of healing and reconstruction. After his assassination, there were differing opinions on how to handle the defeated Confederacy.
Step-by-step explanation:
According to Lincoln, the unknown outcome of the war that was being 'tested' was the future of the South and how the nation would be healed and reconstructed. After his assassination, there were differing opinions on whether the South should be accepted back or punished. The Union had to decide what to do with the defeated Confederacy, and the nation faced challenges in reuniting and constructing a new bi-racial democracy.