Extremely long annotation labels that will not fit in available space.
Another very long label on an adjacent cell.
Two long labels targeting the same cell from different sources.
Labels containing math expressions.
More math labels stacking on nearby cells.
Arrow with no label text – just the arrow pointing between cells.
Mix of empty and non-empty labels on the same target.
Minimal single-character labels on many transitions.
Add long-span annotations with single chars – do they collide with the short ones?
One cell receiving labels of vastly different lengths simultaneously.