Popover: Fix iframe story and add test

packages/components/src/popover/stories/index.tsx

@@ -14,8 +14,8 @@ import { __unstableIframe as Iframe } from '@wordpress/block-editor';
  * Internal dependencies
  */
 import Button from '../../button';
-import { Provider as SlotFillProvider } from '../../slot-fill';
 import { Popover } from '..';
+import { PopoverInsideIframeRenderedInExternalSlot } from '../test/utils';
 import type { PopoverProps } from '../types';
 
 const AVAILABLE_PLACEMENTS: PopoverProps[ 'placement' ][] = [
@@ -249,51 +249,7 @@ DynamicHeight.args = {
 export const WithSlotOutsideIframe: ComponentStory< typeof Popover > = (
 	args
 ) => {
-	const anchorRef = useRef( null );
-	const slotName = 'popover-with-slot-outside-iframe';
-
-	return (
-		<SlotFillProvider>
-			<div>
-				{ /* @ts-expect-error Slot is not currently typed on Popover */ }
-				<Popover.Slot name={ slotName } />
-				<Iframe
-					style={ {
-						width: '100%',
-						height: '400px',
-						border: '0',
-						outline: '1px solid purple',
-					} }
-				>
-					<div
-						style={ {
-							height: '200vh',
-							paddingTop: '10vh',
-						} }
-					>
-						<p
-							style={ {
-								padding: '8px',
-								background: 'salmon',
-								maxWidth: '200px',
-								marginTop: '100px',
-								marginLeft: 'auto',
-								marginRight: 'auto',
-							} }
-							ref={ anchorRef }
-						>
-							Popover&apos;s anchor
-						</p>
-						<Popover
-							{ ...args }
-							__unstableSlotName={ slotName }
-							anchorRef={ anchorRef }
-						/>
-					</div>
-				</Iframe>
-			</div>
-		</SlotFillProvider>
-	);
+	return <PopoverInsideIframeRenderedInExternalSlot { ...args } />;
 };
 WithSlotOutsideIframe.args = {
 	...Default.args,

packages/components/src/popover/test/index.tsx

@@ -19,6 +19,7 @@ import {
 } from '../utils';
 import Popover from '..';
 import type { PopoverProps } from '../types';
+import { PopoverInsideIframeRenderedInExternalSlot } from './utils';
 
 type PositionToPlacementTuple = [
 	NonNullable< PopoverProps[ 'position' ] >,
@@ -175,6 +176,19 @@ describe( 'Popover', () => {
 		} );
 	} );
 
+	describe( 'Slot outside iframe', () => {
+		it( 'should support cross-document rendering', async () => {
+			render(
+				<PopoverInsideIframeRenderedInExternalSlot>
+					<span>content</span>
+				</PopoverInsideIframeRenderedInExternalSlot>
+			);
+			await waitFor( async () =>
+				expect( screen.getByText( 'content' ) ).toBeVisible()
+			);
+		} );
+	} );
+
 	describe( 'positionToPlacement', () => {
 		it.each( ALL_POSITIONS_TO_EXPECTED_PLACEMENTS )(
 			'converts `%s` to `%s`',

packages/components/src/popover/test/utils.tsx

@@ -0,0 +1,80 @@
+/**
+ * WordPress dependencies
+ */
+import { createPortal, useState } from '@wordpress/element';
+
+/**
+ * Internal dependencies
+ */
+import Popover from '..';
+import { Provider as SlotFillProvider } from '../../slot-fill';
+import type { WordPressComponentProps } from '../../ui/context';
+
+const GenericIframe = ( {
+	children,
+	...props
+}: WordPressComponentProps< { children: React.ReactNode }, 'iframe' > ) => {
+	const [ iframeRef, setIframeRef ] = useState< HTMLIFrameElement | null >(
+		null
+	);
+
+	return (
+		<iframe { ...props } title="My Iframe" ref={ setIframeRef }>
+			{ iframeRef?.contentWindow &&
+				createPortal(
+					children,
+					iframeRef?.contentWindow.document.body
+				) }
+		</iframe>
+	);
+};
+
+export const PopoverInsideIframeRenderedInExternalSlot = (
+	props: React.ComponentProps< typeof Popover >
+) => {
+	const SLOT_NAME = 'my-slot';
+	const [ anchorRef, setAnchorRef ] = useState< HTMLParagraphElement | null >(
+		null
+	);
+
+	return (
+		<SlotFillProvider>
+			{ /* @ts-expect-error Slot is not currently typed on Popover */ }
+			<Popover.Slot name={ SLOT_NAME } />
+			<GenericIframe
+				style={ {
+					width: '100%',
+					height: '400px',
+					border: '0',
+					outline: '1px solid purple',
+				} }
+			>
+				<div
+					style={ {
+						height: '200vh',
+						paddingTop: '10vh',
+					} }
+				>
+					<p
+						style={ {
+							padding: '8px',
+							background: 'salmon',
+							maxWidth: '200px',
+							marginTop: '100px',
+							marginLeft: 'auto',
+							marginRight: 'auto',
+						} }
+						ref={ setAnchorRef }
+					>
+						Popover&apos;s anchor
+					</p>
+					<Popover
+						{ ...props }
+						__unstableSlotName={ SLOT_NAME }
+						anchor={ anchorRef }
+					/>
+				</div>
+			</GenericIframe>
+		</SlotFillProvider>
+	);
+};