fix: serialize mutation records

Author: eps1lon

src/__tests__/__snapshots__/wait-for-dom-change.js.snap

@@ -2,12 +2,34 @@
 
 exports[`timers works with fake timers 1`] = `
 Array [
-  MutationRecord {},
+  Object {
+    "addedNodes": NodeList [],
+    "attributeName": "id",
+    "attributeNamespace": null,
+    "nextSibling": null,
+    "oldValue": null,
+    "previousSibling": null,
+    "removedNodes": NodeList [],
+    "target": <div
+      id="foo"
+    />,
+  },
 ]
 `;
 
 exports[`timers works with real timers 1`] = `
 Array [
-  MutationRecord {},
+  Object {
+    "addedNodes": NodeList [],
+    "attributeName": "id",
+    "attributeNamespace": null,
+    "nextSibling": null,
+    "oldValue": null,
+    "previousSibling": null,
+    "removedNodes": NodeList [],
+    "target": <div
+      id="foo"
+    />,
+  },
 ]
 `;

src/__tests__/wait-for-dom-change.js

@@ -19,7 +19,18 @@ test('waits for the dom to change in the document', async () => {
   const mutationResult = await promise
   expect(mutationResult).toMatchInlineSnapshot(`
     Array [
-      MutationRecord {},
+      Object {
+        "addedNodes": NodeList [],
+        "attributeName": "id",
+        "attributeNamespace": null,
+        "nextSibling": null,
+        "oldValue": null,
+        "previousSibling": null,
+        "removedNodes": NodeList [],
+        "target": <div
+          id="foo"
+        />,
+      },
     ]
   `)
 })
@@ -31,7 +42,18 @@ test('waits for the dom to change in a specified container', async () => {
   const mutationResult = await promise
   expect(mutationResult).toMatchInlineSnapshot(`
     Array [
-      MutationRecord {},
+      Object {
+        "addedNodes": NodeList [],
+        "attributeName": "id",
+        "attributeNamespace": null,
+        "nextSibling": null,
+        "oldValue": null,
+        "previousSibling": null,
+        "removedNodes": NodeList [],
+        "target": <div
+          id="foo"
+        />,
+      },
     ]
   `)
 })

tests/setup-env.js

@@ -2,3 +2,25 @@ import '@testing-library/jest-dom/extend-expect'
 import jestSerializerAnsi from 'jest-serializer-ansi'
 
 expect.addSnapshotSerializer(jestSerializerAnsi)
+// add serializer for MutationRecord
+expect.addSnapshotSerializer({
+  print: (record, serialize) => {
+    return serialize({
+      addedNodes: record.addedNodes,
+      attributeName: record.attributeName,
+      attributeNamespace: record.attributeNamespace,
+      nextSibling: record.nextSibling,
+      oldValue: record.oldValue,
+      previousSibling: record.previousSibling,
+      removedNodes: record.removedNodes,
+      target: record.target,
+    })
+  },
+  test: value => {
+    // list of records will stringify to the same value
+    return (
+      Array.isArray(value) === false &&
+      String(value) === '[object MutationRecord]'
+    )
+  },
+})