Improve code coverage

src/utils/ViewHeightSensor.test.tsx

@@ -0,0 +1,11 @@
+// SPDX-License-Identifier: MIT
+// Copyright (c) 2021 The Pybricks Authors
+
+import { render } from '@testing-library/react';
+import React from 'react';
+import ViewHeightSensor from './ViewHeightSensor';
+
+it('should set the --pb-vh variable on resize', () => {
+    render(<ViewHeightSensor />);
+    // REVISIT: it is not easy to test the resize event since jest-dom doesn't do layout
+});

src/utils/monkey-patch.ts

@@ -26,6 +26,7 @@ export function useTooltip2MonkeyPatch<T>(): React.RefObject<Tooltip2<T>> {
     const tooltipRef = useRef<Tooltip2<T>>(null);
 
     useEffect(() => {
+        // istanbul ignore if: should not happen ever
         if (!tooltipRef.current) {
             return;
         }
@@ -55,6 +56,7 @@ export function useTooltip2MonkeyPatch<T>(): React.RefObject<Tooltip2<T>> {
  * @param tooltipRef The reference returned from useTooltip2MonkeyPatch()
  */
 export function closeTooltip2<T>(tooltipRef: React.RefObject<Tooltip2<T>>): void {
+    // istanbul ignore if: should not happen ever
     if (!tooltipRef.current) {
         return;
     }