Add colour attribute to nodes in tests.

tests/test_first-permissible-or-none-node.py

@@ -7,6 +7,7 @@ def test_first_permissible_or_none_node():
     G = nx.complete_graph(3)
     permissible_dict = {0: [0, 1], 1: [1, 2], 2: [2, 3]}
     nx.set_node_attributes(G, permissible_dict, "permissible")
+    nx.set_node_attributes(G, None, "colour")
     assert first_permissible_or_none_node(G, 0) == 0
     assert first_permissible_or_none_node(G, 1) == 1
-    assert first_permissible_or_node_node(G, 2) == 2
+    assert first_permissible_or_none_node(G, 2) == 2