Added graph dfs challenge.

graphs_trees/graph_dfs/test_dfs.py

@@ -0,0 +1,34 @@
+from nose.tools import assert_equal
+
+
+class TestDfs(object):
+
+    def __init__(self):
+        self.results = Results()
+
+    def test_dfs(self):
+        nodes = []
+        graph = Graph()
+        for id in range(0, 6):
+            nodes.append(graph.add_node(id))
+        graph.add_edge(0, 1, 5)
+        graph.add_edge(0, 4, 3)
+        graph.add_edge(0, 5, 2)
+        graph.add_edge(1, 3, 5)
+        graph.add_edge(1, 4, 4)
+        graph.add_edge(2, 1, 6)
+        graph.add_edge(3, 2, 7)
+        graph.add_edge(3, 4, 8)
+        dfs(nodes[0], self.results.add_result)
+        assert_equal(str(self.results), "[0, 1, 3, 2, 4, 5]")
+
+        print('Success: test_dfs')
+
+
+def main():
+    test = TestDfs()
+    test.test_dfs()
+
+
+if __name__ == '__main__':
+    main()