Issue #24 Updated GraphEdgeError to produce a readable output, added test

Author: wwxiao09

src/dalpy/graphs.py

@@ -119,13 +119,13 @@ def __init__(self, vertex_name):
         Args:
             vertex_name: The string name of the `Vertex` this `GraphVertexError` is being raised in association with.
         """
-        super().__init__(f'graph does not have vertex with name {vertex_name}')
+        super().__init__(f'graph does not have vertex with name "{vertex_name}"')
 
 
 class GraphEdgeError(Exception):
     """This class is used by `Graph` to raise errors regarding invalid edges."""
 
-    def __init__(self, source_name, dest_name):
+    def __init__(self, source, dest):
         """Initializes a `GraphEdgeError` that will be raised associated with a particular `Vertex`.
 
         Args:
@@ -135,7 +135,7 @@ def __init__(self, source_name, dest_name):
                        in association with.
         """
         super().__init__(
-            f'graph does not have an edge from a vertex with name {source_name} to a vertex with name {dest_name}')
+            f'graph does not have an edge from a vertex with name "{source.get_name()}" to a vertex with name "{dest.get_name()}"')
 
 
 class Graph:

tests/graph_tests.py

@@ -131,6 +131,18 @@ def test_unweighted_edge(self):
         g.add_edge(a, b)
         self.assertIsNone(g.weight(a, b))
 
+    def test_GraphEdgeError(self):
+        g = Graph()
+        a = Vertex('a')
+        b = Vertex('b')
+        g.add_vertex(a)
+        g.add_vertex(b)
+        try:
+            g.weight(b, a)
+        except GraphEdgeError as e:
+            self.assertEqual(e.args[0], "graph does not have an edge from a vertex with name \"b\" to a vertex with name \"a\"")
+
+
 
 if __name__ == '__main__':
     unittest.main()