Add test to ensure we do nothing if migrations fail during serialization

rbx_xml/src/tests/basic.rs

@@ -334,3 +334,14 @@ fn migrated_properties() {
     crate::to_writer_default(&mut encoded, &tree, &[tree.root_ref()]).unwrap();
     insta::assert_snapshot!(std::str::from_utf8(&encoded).unwrap());
 }
+
+#[test]
+fn bad_migrated_property() {
+    let tree = WeakDom::new(InstanceBuilder::new("Folder").with_children([
+        InstanceBuilder::new("TextLabel").with_property("Font", Enum::from_u32(u32::MAX)),
+    ]));
+
+    let mut encoded = Vec::new();
+    crate::to_writer_default(&mut encoded, &tree, &[tree.root_ref()]).unwrap();
+    insta::assert_snapshot!(std::str::from_utf8(&encoded).unwrap());
+}

rbx_xml/src/tests/snapshots/rbx_xml__tests__basic__bad_migrated_property.snap

@@ -0,0 +1,17 @@
+---
+source: rbx_xml/src/tests/basic.rs
+expression: "std::str::from_utf8(&encoded).unwrap()"
+---
+<roblox version="4">
+  <Item class="Folder" referent="0">
+    <Properties>
+      <string name="Name">Folder</string>
+    </Properties>
+    <Item class="TextLabel" referent="1">
+      <Properties>
+        <string name="Name">TextLabel</string>
+        <token name="Font">4294967295</token>
+      </Properties>
+    </Item>
+  </Item>
+</roblox>