No vertices:
Result:      NaN
Unconnected pairs:        0

One vertex:
Result:      NaN
Unconnected pairs:        0

Two vertices:
Result:      NaN
Unconnected pairs:        2

Two vertices, inf for unconnected pairs:
Result:      Inf
Unconnected pairs:        2

Smallest bifurcating directed tree:
Result:        1
Unconnected pairs:        4

Smallest bifurcating directed tree, inf for unconnected pairs:
Result:      Inf
Unconnected pairs:        4

Graph with loops and multiple edges:
Result:        5
Unconnected pairs:       19

Graph with loops and multiple edges, ignoring direction:
Result:      4.6
Unconnected pairs:       10

Checking incorrect weight length error handling.
Checking negative weight error handling.