Write tests and ensure adding instances works

rojo-test/serve-test-snapshots/serve_test__add_folder_all-2.snap

@@ -0,0 +1,26 @@
+---
+source: rojo-test/src/serve_test.rs
+expression: "read_response.intern_and_redact(&mut redactions, root_id)"
+---
+instances:
+  id-2:
+    Id: id-2
+    Parent: ~
+    Name: add_folder
+    ClassName: Folder
+    Properties: {}
+    Children:
+      - id-3
+    Metadata:
+      ignoreUnknownInstances: false
+  id-3:
+    Id: id-3
+    Parent: id-2
+    Name: my-new-folder
+    ClassName: Folder
+    Properties: {}
+    Children: []
+    Metadata:
+      ignoreUnknownInstances: false
+messageCursor: 1
+sessionId: id-1