testing: vertically center test message badge

Closes #234287

src/vs/workbench/contrib/testing/browser/testingDecorations.ts

@@ -1332,6 +1332,8 @@ class TestMessageDecoration implements ITestDecoration {
 	}
 }
 
+const ERROR_CONTENT_WIDGET_HEIGHT = 20;
+
 class TestErrorContentWidget extends Disposable implements IContentWidget {
 	private readonly id = generateUuid();
 
@@ -1360,6 +1362,18 @@ class TestErrorContentWidget extends Disposable implements IContentWidget {
 	) {
 		super();
 
+		const setMarginTop = () => {
+			const lineHeight = editor.getOption(EditorOption.lineHeight);
+			this.node.root.style.marginTop = (lineHeight - ERROR_CONTENT_WIDGET_HEIGHT) / 2 + 'px';
+		};
+
+		setMarginTop();
+		this._register(editor.onDidChangeConfiguration(e => {
+			if (e.hasChanged(EditorOption.lineHeight)) {
+				setMarginTop();
+			}
+		}));
+
 		let text: string;
 		if (message.expected !== undefined && message.actual !== undefined) {
 			text = `${truncateMiddle(message.actual, 15)} != ${truncateMiddle(message.expected, 15)}`;