Tests: Adds test to data-nimg data attribute based on layout prop. (#…

…28444)

Adds tests to the Image component to verify that the correct data is being exposed.
Based on #27899 and #28312

## Bug

- [ ] Related issues linked using `fixes #number`
- [x] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have helpful link attached, see `contributing.md`

## Documentation / Examples

- [ ] Make sure the linting passes

test/integration/image-component/basic/test/index.test.js

@@ -308,6 +308,14 @@ describe('Image Component Tests', () => {
     it('should not create any preload tags higher up the page than CSS preload tags', async () => {
       expect(await hasImagePreloadBeforeCSSPreload()).toBe(false)
     })
+    it('should add data-nimg data attribute based on layout', async () => {
+      expect(
+        await browser.elementById('image-with-sizes').getAttribute('data-nimg')
+      ).toBe('responsive')
+      expect(
+        await browser.elementById('basic-image').getAttribute('data-nimg')
+      ).toBe('intrinsic')
+    })
   })
   describe('Client-side Image Component Tests', () => {
     beforeAll(async () => {