Null graph:
Average shortest path length: NaN
No. of unconnected pairs: 0

Singleton graph:
Average shortest path length: NaN
No. of unconnected pairs: 0

2-vertex empty graph, unconn=true:
Average shortest path length: NaN
No. of unconnected pairs: 2

2-vertex empty graph, unconn=false:
Average shortest path length: Inf
No. of unconnected pairs: 2

Smallest bifurcating directed tree, unconn=true:
Average shortest path length: 1
No. of unconnected pairs: 4

Smallest bifurcating directed tree, unconn=false:
Average shortest path length: 1
No. of unconnected pairs: 4

Undirected 11-cycle:
Average shortest path length: 3
No. of unconnected pairs: 0

Directed 6-cycle:
Average shortest path length: 5.5
No. of unconnected pairs: 0

De Bruijn graph, n=3 and m=5:
Average shortest path length: 4.34405
No. of unconnected pairs: 0