Add an assertion when updating conversations; update cleanData

ts/test-both/util/assert_test.ts

@@ -0,0 +1,18 @@
+// Copyright 2021 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import * as chai from 'chai';
+
+import { assert } from '../../util/assert';
+
+describe('assert', () => {
+  it('does nothing if the assertion passes', () => {
+    assert(true, 'foo bar');
+  });
+
+  it("throws because we're in a test environment", () => {
+    chai.assert.throws(() => {
+      assert(false, 'foo bar');
+    }, 'foo bar');
+  });
+});