src/vs/platform/driver/browser/baseDriver.ts/BaseWindowDriver/isActiveElement
class BaseWindowDriver:	async isActiveElement(selector: string): Promise<boolean> {
		const element = document.querySelector(selector);

		if (element !== document.activeElement) {
			const chain: string[] = [];
			let el = document.activeElement;

			while (el) {
				const tagName = el.tagName;
				const id = el.id ? `#${el.id}` : '';
				const classes = coalesce(el.className.split(/\s+/g).map(c => c.trim())).map(c => `.${c}`).join('');
				chain.unshift(`${tagName}${id}${classes}`);

				el = el.parentElement;
			}

			throw new Error(`Active element not found. Current active element is '${chain.join(' > ')}'. Looking for ${selector}`);
		}

		return true;
	}