Null graph:
( )

Singleton graph:
( 0 )

Path with isolated vertex:
( 1 0 1 )

Undirected path graph:
( 4 3 2 3 4 )

Directed path graph:
( 4 3 2 1 0 )

Undirected star:
( 1 2 2 2 2 2 2 2 2 2 )

Out-star:
( 1 2 2 2 2 2 2 2 2 2 )

Out-star, IGRAPH_OUT:
( 1 0 0 0 0 0 0 0 0 0 )

Out-star with NULL weights:
( 1 2 2 2 2 2 2 2 2 2 )

Out-star with weights:
( 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.7 )

Check wrong number of weights error.
Check NaN weight error.
Check negative weight error.
