0x0 matrix:
directed: true
vcount: 0
edges: {
}

1x1 matrix, no loops:
directed: true
vcount: 1
edges: {
}

1x1 matrix, loops once:
directed: true
vcount: 1
edges: {
0 0
}

1x1 matrix, loops twice (treated as loops once):
directed: true
vcount: 1
edges: {
0 0
}

3x3 matrix, IGRAPH_ADJ_DIRECTED, no loops:
directed: true
vcount: 3
edges: {
0 1
0 1
1 0
1 0
1 0
1 2
1 2
1 2
1 2
2 1
2 1
2 1
2 1
2 1
}

3x3 matrix, IGRAPH_ADJ_DIRECTED, loops once:
directed: true
vcount: 3
edges: {
0 0
0 0
0 0
0 0
0 1
0 1
1 0
1 0
1 0
1 2
1 2
1 2
1 2
2 1
2 1
2 1
2 1
2 1
2 2
2 2
2 2
2 2
2 2
2 2
}

3x3 matrix, IGRAPH_ADJ_DIRECTED, loops twice (treated as loops once):
directed: true
vcount: 3
edges: {
0 0
0 0
0 0
0 0
0 1
0 1
1 0
1 0
1 0
1 2
1 2
1 2
1 2
2 1
2 1
2 1
2 1
2 1
2 2
2 2
2 2
2 2
2 2
2 2
}

3x3 matrix, IGRAPH_ADJ_UNDIRECTED, no loops:
directed: false
vcount: 3
edges: {
0 1
0 1
1 2
1 2
1 2
1 2
}

3x3 matrix, IGRAPH_ADJ_UNDIRECTED, loops once:
directed: false
vcount: 3
edges: {
0 0
0 0
0 0
0 0
0 1
0 1
1 2
1 2
1 2
1 2
2 2
2 2
2 2
2 2
2 2
2 2
}

3x3 matrix, IGRAPH_ADJ_UNDIRECTED, loops twice:
directed: false
vcount: 3
edges: {
0 0
0 0
0 1
0 1
1 2
1 2
1 2
1 2
2 2
2 2
2 2
}

3x3 matrix, IGRAPH_ADJ_MAX, no loops:
directed: false
vcount: 3
edges: {
0 1
0 1
0 1
1 2
1 2
1 2
1 2
1 2
}

3x3 matrix, IGRAPH_ADJ_MAX, loops once:
directed: false
vcount: 3
edges: {
0 0
0 0
0 0
0 0
0 1
0 1
0 1
1 2
1 2
1 2
1 2
1 2
2 2
2 2
2 2
2 2
2 2
2 2
}

3x3 matrix, IGRAPH_ADJ_MAX, loops twice:
directed: false
vcount: 3
edges: {
0 0
0 0
0 1
0 1
0 1
1 2
1 2
1 2
1 2
1 2
2 2
2 2
2 2
}

3x3 matrix, IGRAPH_ADJ_MIN, no loops:
directed: false
vcount: 3
edges: {
0 1
0 1
1 2
1 2
1 2
1 2
}

3x3 matrix, IGRAPH_ADJ_MIN, loops once:
directed: false
vcount: 3
edges: {
0 0
0 0
0 0
0 0
0 1
0 1
1 2
1 2
1 2
1 2
2 2
2 2
2 2
2 2
2 2
2 2
}

3x3 matrix, IGRAPH_ADJ_MIN, loops twice:
directed: false
vcount: 3
edges: {
0 0
0 0
0 1
0 1
1 2
1 2
1 2
1 2
2 2
2 2
2 2
}

3x3 matrix, IGRAPH_ADJ_PLUS, no loops:
directed: false
vcount: 3
edges: {
0 1
0 1
0 1
0 1
0 1
1 2
1 2
1 2
1 2
1 2
1 2
1 2
1 2
1 2
}

3x3 matrix, IGRAPH_ADJ_PLUS, loops once:
directed: false
vcount: 3
edges: {
0 0
0 0
0 0
0 0
0 1
0 1
0 1
0 1
0 1
1 2
1 2
1 2
1 2
1 2
1 2
1 2
1 2
1 2
2 2
2 2
2 2
2 2
2 2
2 2
}

3x3 matrix, IGRAPH_ADJ_PLUS, loops twice:
directed: false
vcount: 3
edges: {
0 0
0 0
0 1
0 1
0 1
0 1
0 1
1 2
1 2
1 2
1 2
1 2
1 2
1 2
1 2
1 2
2 2
2 2
2 2
}

3x3 matrix, IGRAPH_ADJ_UPPER, no loops:
directed: false
vcount: 3
edges: {
0 1
0 1
1 2
1 2
1 2
1 2
}

3x3 matrix, IGRAPH_ADJ_UPPER, loops once:
directed: false
vcount: 3
edges: {
0 0
0 0
0 0
0 0
0 1
0 1
1 2
1 2
1 2
1 2
2 2
2 2
2 2
2 2
2 2
2 2
}

3x3 matrix, IGRAPH_ADJ_UPPER, loops twice (treated as loops once):
directed: false
vcount: 3
edges: {
0 0
0 0
0 0
0 0
0 1
0 1
1 2
1 2
1 2
1 2
2 2
2 2
2 2
2 2
2 2
2 2
}

3x3 matrix, IGRAPH_ADJ_LOWER, no loops:
directed: false
vcount: 3
edges: {
0 1
0 1
0 1
1 2
1 2
1 2
1 2
1 2
}

3x3 matrix, IGRAPH_ADJ_LOWER, loops once:
directed: false
vcount: 3
edges: {
0 0
0 0
0 0
0 0
0 1
0 1
0 1
1 2
1 2
1 2
1 2
1 2
2 2
2 2
2 2
2 2
2 2
2 2
}

3x3 matrix, IGRAPH_ADJ_LOWER, loops twice (treated as loops once):
directed: false
vcount: 3
edges: {
0 0
0 0
0 0
0 0
0 1
0 1
0 1
1 2
1 2
1 2
1 2
1 2
2 2
2 2
2 2
2 2
2 2
2 2
}

Check handling of non-square matrix error.

Check handling of negative number of edges error.

Check handling of odd number in diagonal.

Check handling of invalid adjacency mode.

Check handling of non-symmetric matrix for IGRAPH_ADJ_UNDIRECTED.