Checking vs_none vertex selector:
Checking vector selector:
Some graph:
2
3
4
Edgeless graph:
2
3
4
Graph without vertices should fail.
Vertex selector with negative index should fail
Checking copy vector selector:
Some graph:
2
3
4
Edgeless graph:
2
3
4
Copy of vs:
2
3
4
Graph without vertices should fail.
As vector should give all 5 vertices:
0 1 2 3 4
As vector should give 0 vertices:

Checking vs_range:
2
3
4
Checking vss_range using vs_range parameters:
2
3
4
Checking whether vss_range accepts an empty range.
