public void EdgeExists()
{
var myGraph = new UndirectedWeightedGraph <int, EdgeData>();
myGraph.AddNodes(1, 2, 3);
myGraph.AddEdges(
(1, 2, 4, dummyEdgeData),
(2, 3, 5, dummyEdgeData)
);
myGraph.Exists(1, 2).Should().BeTrue();
myGraph.Exists(2, 1).Should().BeTrue();
myGraph.Exists(2, 3).Should().BeTrue();
myGraph.Exists(3, 2).Should().BeTrue();
myGraph.Exists(1, 3).Should().BeFalse();
myGraph.Invoking(x => x.Exists(3, 4)).Should().Throw <ArgumentException>();
}