diff --git a/graph.rkt b/graph.rkt
index fb2fee5..25fd6ee 100644
--- a/graph.rkt
+++ b/graph.rkt
@@ -70,9 +70,10 @@
 
   (test-case "1 Generic Graph Interface"
     (define g (directed-graph '((a b) (b c))))
-    (check-true (has-edge? g 'a 'c))
+    (check-false (has-edge? g 'a 'c))
     (check-true (has-vertex? g 'a)))
 
   (test-case "10 Graphviz"
     (define g (directed-graph '((a b) (b c))))
-    (graphviz g)))
+    (check-equal? (graphviz g)
+                  "digraph G {\n\tnode0 [label=\"c\"];\n\tnode1 [label=\"b\"];\n\tnode2 [label=\"a\"];\n\tsubgraph U {\n\t\tedge [dir=none];\n\t}\n\tsubgraph D {\n\t\tnode1 -> node0;\n\t\tnode2 -> node1;\n\t}\n}\n")))