public void ToString_error()
{
Graph1 g = new Graph1();
g.AddNode("Kyiv");
g.AddNode("Lviv");
Assert.AreEqual("Kyiv Lviv ", g.ToString());
}
public void ToStringEmpty_error()
{
Graph1 g = new Graph1();
Assert.Throws(typeof(InvalidOperationException), () => g.ToString());
}
