Function watch

test/MultiCompiler.test.js:373–387

(
					files,
					directories,
					missing,
					startTime,
					options,
					callback,
					callbackUndelayed
				)

		compiler.watchFileSystem =
			/** @type {import("../lib/util/fs").WatchFileSystem} */ ({
				watch(
					files,
					directories,
					missing,
					startTime,
					options,
					callback,
					callbackUndelayed
				) {
					watchCallbacks.push(callback);
					watchCallbacksUndelayed.push(callbackUndelayed);
					return /** @type {import("../lib/util/fs").Watcher} */ (
						/** @type {unknown} */ (undefined)
					);
				}
			});
		/** @type {string[]} */
		const events = [];