Merge pull request #12047 from ckeditor/ck/11115-incorrect-aria-press…

…ed-in-switch

Fix (ui): The default value of the `aria-pressed` DOM attribute of a [toggleable](https://ckeditor.com/docs/ckeditor5/latest/api/module_ui_button_button-Button.html#member-isToggleable) button should be `false` instead of `undefined`. Closes #11115.

packages/ckeditor5-ui/src/button/buttonview.js

@@ -145,7 +145,7 @@ export default class ButtonView extends View {
 				tabindex: bind.to( 'tabindex' ),
 				'aria-labelledby': `ck-editor__aria-label_${ ariaLabelUid }`,
 				'aria-disabled': bind.if( 'isEnabled', true, value => !value ),
-				'aria-pressed': bind.to( 'isOn', value => this.isToggleable ? String( value ) : false )
+				'aria-pressed': bind.to( 'isOn', value => this.isToggleable ? String( !!value ) : false )
 			},
 
 			children: this.children,

packages/ckeditor5-ui/tests/button/buttonview.js

@@ -262,6 +262,12 @@ describe( 'ButtonView', () => {
 				expect( view.element.attributes[ 'aria-disabled' ].value ).to.equal( 'true' );
 			} );
 
+			it( '-pressed has correct default value for toggleable button', () => {
+				view.isToggleable = true;
+				view.isOn = undefined;
+				expect( view.element.attributes[ 'aria-pressed' ].value ).to.equal( 'false' );
+			} );
+
 			it( '-pressed reacts to #isOn', () => {
 				view.isToggleable = true;
 				view.isOn = true;