Message details: group by send status, including viewed state

ts/test-both/util/mapUtil_test.ts

@@ -0,0 +1,30 @@
+// Copyright 2021 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import { assert } from 'chai';
+import * as sinon from 'sinon';
+
+import { groupBy } from '../../util/mapUtil';
+
+describe('map utilities', () => {
+  describe('groupBy', () => {
+    it('returns an empty map when passed an empty iterable', () => {
+      const fn = sinon.fake();
+
+      assert.isEmpty(groupBy([], fn));
+
+      sinon.assert.notCalled(fn);
+    });
+
+    it('groups the iterable', () => {
+      assert.deepEqual(
+        groupBy([2.3, 1.3, 2.9, 1.1, 3.4], Math.floor),
+        new Map([
+          [1, [1.3, 1.1]],
+          [2, [2.3, 2.9]],
+          [3, [3.4]],
+        ])
+      );
+    });
+  });
+});