Fixes warnings in some tests (#2241)

Signed-off-by: Tilman Vatteroth <git@tilmanvatteroth.de>

src/utils/wait-for-other-promises-to-finish.ts

@@ -0,0 +1,17 @@
+/*
+ * SPDX-FileCopyrightText: 2022 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+/**
+ * Waits until all other pending promises are processed.
+ *
+ * NodeJS has a queue for async code that waits for being processed. This method adds a promise to the very end of this queue.
+ * If the promise is resolved then this means that all other promises before it have been processed as well.
+ *
+ * @return A promise which resolves when all other promises have been processed
+ */
+export function waitForOtherPromisesToFinish(): Promise<void> {
+  return new Promise((resolve) => process.nextTick(resolve))
+}