Timeline: repair oldest/newest metrics if we fetch nothing

ts/test-node/util/getOwn_test.ts

@@ -0,0 +1,50 @@
+// Copyright 2020 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import { assert } from 'chai';
+
+import { getOwn } from '../../util/getOwn';
+
+describe('getOwn', () => {
+  class Person {
+    public birthYear: number;
+
+    constructor(birthYear: number) {
+      this.birthYear = birthYear;
+    }
+
+    getAge() {
+      return new Date().getFullYear() - this.birthYear;
+    }
+  }
+
+  it('returns undefined when asking for a non-existent property', () => {
+    const obj: Record<string, number> = { bar: 123 };
+    assert.isUndefined(getOwn(obj, 'foo'));
+  });
+
+  it('returns undefined when asking for a non-own property', () => {
+    const obj: Record<string, number> = { bar: 123 };
+    assert.isUndefined(getOwn(obj, 'hasOwnProperty'));
+
+    const person = new Person(1880);
+    assert.isUndefined(getOwn(person, 'getAge'));
+  });
+
+  it('returns own properties', () => {
+    const obj: Record<string, number> = { foo: 123 };
+    assert.strictEqual(getOwn(obj, 'foo'), 123);
+
+    const person = new Person(1880);
+    assert.strictEqual(getOwn(person, 'birthYear'), 1880);
+  });
+
+  it('works even if `hasOwnProperty` has been overridden for the object', () => {
+    const obj: Record<string, unknown> = {
+      foo: 123,
+      hasOwnProperty: () => true,
+    };
+    assert.strictEqual(getOwn(obj, 'foo'), 123);
+    assert.isUndefined(getOwn(obj, 'bar'));
+  });
+});