What observational evidence would suggest a finite, multi-connected topology like a torus?

Answer

Seeing duplicate images of the same distant galaxies or repeating patterns in the CMB

If the universe were a torus smaller than the distance light has traveled since the Big Bang, we would expect to see repeating structures or echoes in the sky, such as duplicate galaxy images or CMB patterns.

What observational evidence would suggest a finite, multi-connected topology like a torus?
structureuniverseGeometrycosmologyshape