test(palette): fix DOM fragment and image mock compatibility after rebase

- ensure createDocumentFragment returns real DOM nodes
- fix img.style reference in createElement mock
- align mocks with jsdom behavior to prevent appendChild errors

Author: mahesh-09-12

js/__tests__/palette.test.js

@@ -1369,7 +1369,7 @@ describe("Palettes Class", () => {
                 if (tag === "img") {
                     const img = realCreate.call(document, "img");
                     img.width = 50;
-                    image.style = {};
+                    img.style = {};
                     return img;
                 }
                 return realCreate.call(document, tag);
@@ -1406,9 +1406,11 @@ describe("Palettes Class", () => {
             const paletteList = {
                 appendChild: jest.fn()
             };
-            document.createDocumentFragment = jest.fn(() => ({
-                appendChild: jest.fn()
-            }));
+            const realCreateFragment = document.createDocumentFragment;
+
+            document.createDocumentFragment = jest.fn(() => {
+                return realCreateFragment.call(document);
+            });
 
             global.docById = jest.fn(id => {
                 if (id === "PaletteBody_items") return paletteList;
@@ -1502,9 +1504,11 @@ describe("Palettes Class", () => {
             const paletteList = {
                 appendChild: jest.fn()
             };
-            document.createDocumentFragment = jest.fn(() => ({
-                appendChild: jest.fn()
-            }));
+            const realCreateFragment = document.createDocumentFragment;
+
+            document.createDocumentFragment = jest.fn(() => {
+                return realCreateFragment.call(document);
+            });
 
             global.docById = jest.fn(id => {
                 if (id === "PaletteBody_items") return paletteList;