fix compiler test

d2compiler/compile_test.go

@@ -1561,7 +1561,10 @@ dst.id <-> src.dst_id
 			text: `x -> x
 `,
 			assertions: func(t *testing.T, g *d2graph.Graph) {
-				diff.AssertStringEq(t, g.Edges[0].Dst.ID, g.Edges[0].Src.ID)
+				_, err := diff.Strings(g.Edges[0].Dst.ID, g.Edges[0].Src.ID)
+				if err != nil {
+					t.Fatal(err)
+				}
 			},
 		},
 	}

testdata/d2compiler/TestCompile/self-referencing.exp.json

@@ -68,9 +68,10 @@
           "value": ""
         },
         "direction": {
-          "value": "down"
+          "value": ""
         }
-      }
+      },
+      "zIndex": 0
     },
     "edges": [
       {
@@ -101,7 +102,8 @@
           "direction": {
             "value": ""
           }
-        }
+        },
+        "zIndex": 0
       }
     ],
     "objects": [
@@ -164,9 +166,10 @@
             "value": ""
           },
           "direction": {
-            "value": "down"
+            "value": ""
           }
-        }
+        },
+        "zIndex": 0
       }
     ]
   },