Timeline: repair oldest/newest metrics if we fetch nothing

ts/test-both/state/selectors/items_test.ts

@@ -0,0 +1,40 @@
+// Copyright 2020 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import { assert } from 'chai';
+import { getPinnedConversationIds } from '../../../state/selectors/items';
+import type { StateType } from '../../../state/reducer';
+
+describe('both/state/selectors/items', () => {
+  describe('#getPinnedConversationIds', () => {
+    // Note: we would like to use the full reducer here, to get a real empty state object
+    //   but we cannot load the full reducer inside of electron-mocha.
+    function getDefaultStateType(): StateType {
+      return {
+        items: {},
+        // eslint-disable-next-line @typescript-eslint/no-explicit-any
+      } as any;
+    }
+
+    it('returns pinnedConversationIds key from items', () => {
+      const expected = ['one', 'two'];
+      const state: StateType = {
+        ...getDefaultStateType(),
+        items: {
+          pinnedConversationIds: expected,
+        },
+      };
+
+      const actual = getPinnedConversationIds(state);
+      assert.deepEqual(actual, expected);
+    });
+
+    it('returns empty array if no saved data', () => {
+      const expected: Array<string> = [];
+      const state = getDefaultStateType();
+
+      const actual = getPinnedConversationIds(state);
+      assert.deepEqual(actual, expected);
+    });
+  });
+});