Add graph references

references/igraph-1.0.1/tests/unit/graph1.gml

@@ -0,0 +1,44 @@
+# comment lines are ignored
+Version 1
+graph [
+    directed 1
+    node [
+        id 1
+        a [ b 1 ]
+        b +2
+        c 5.6
+        graphics [ x 0 y 0 ]
+    ]
+    node [
+        a 1
+        id 2
+        a 2
+        b "asd"
+        d -Inf
+        nan "foo"
+    ]
+    edge [
+        source 5 target 1
+        weight -0.45
+        label -0.45
+        num1 NAN
+    ]
+    node [
+        id 5
+        c [ str "bar" ]
+    ]
+    edge [
+        source 2 target 5
+        label "Tom & Jerry's "friendship""
+# The 'sou_rce' attribute will be ignored by the GML writer as it would conflict with
+# 'source' after stripping the '_' character.
+        sou_rce 1.0
+        num1 +inF
+    ]
+    AttOne 1
+    AttOne "x"
+    AttTwo 3.14
+]
+
+# second graph is ignored
+graph [ node [ ] ]