@@ -11,12 +11,18 @@ import { dispatch } from '@wordpress/data';
 import border, {
 	applyBorderStyleDefaults,
 	getBorderStyleFallbacks,
-	getInheritedBorderStyles,
+	getInheritedBorderStyles as getInheritedBorderStylesFromSource,
 } from '../border';
 import { store as blockEditorStore } from '../../store';
 import { globalStylesDataKey } from '../../store/private-keys';
 import { unlock } from '../../lock-unlock';
 
+// The JSDoc marks both subtrees as required, but callers pass `undefined` for a missing level.
+const getInheritedBorderStyles = getInheritedBorderStylesFromSource as (
+	blockBorder?: object,
+	variationBorder?: object
+) => ReturnType< typeof getInheritedBorderStylesFromSource >;
+
 vi.mock(
 	import( '../../components/use-settings' ),
 	async ( importOriginal ) => ( {
@@ -284,6 +290,7 @@ describe( 'getBorderStyleFallbacks', () => {
 	} );
 
 	it( 'returns empty when called with no arguments', () => {
+		// @ts-expect-error The missing arguments are deliberate.
 		expect( getBorderStyleFallbacks() ).toEqual( {} );
 	} );
 
@@ -439,18 +446,23 @@ describe( 'border useBlockProps', () => {
 	const widthOnly = { border: { width: '2px' } };
 
 	// `updateSettings` drops symbol keys, so set the private key directly.
-	function setGlobalStyles( styles ) {
+	function setGlobalStyles( styles: Record< string, unknown > | undefined ) {
 		unlock( dispatch( blockEditorStore ) ).__experimentalUpdateSettings( {
 			[ globalStylesDataKey ]: styles,
 		} );
 	}
 
-	function getStyle( props ) {
+	type BorderBlockProps = Parameters< typeof border.useBlockProps >[ 0 ];
+
+	function getStyle( props: Partial< BorderBlockProps > ) {
 		const { result, unmount } = renderHook( () =>
-			border.useBlockProps( { name: BLOCK_NAME, ...props } )
+			border.useBlockProps( {
+				name: BLOCK_NAME,
+				...props,
+			} as BorderBlockProps )
 		);
 		unmount();
-		return result.current.style;
+		return ( result.current as { style?: Record< string, string > } ).style;
 	}
 
 	beforeEach( () => {