Timeline: repair oldest/newest metrics if we fetch nothing

ts/test-node/util/getAnimatedPngDataIfExists_test.ts

@@ -0,0 +1,60 @@
+// Copyright 2020 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import * as fs from 'fs';
+import * as path from 'path';
+import { assert } from 'chai';
+
+import { getAnimatedPngDataIfExists } from '../../util/getAnimatedPngDataIfExists';
+
+describe('getAnimatedPngDataIfExists', () => {
+  const fixture = (filename: string): Promise<Buffer> => {
+    const fixturePath = path.join(
+      __dirname,
+      '..',
+      '..',
+      '..',
+      'fixtures',
+      filename
+    );
+    return fs.promises.readFile(fixturePath);
+  };
+
+  it('returns null for empty buffers', () => {
+    assert.isNull(getAnimatedPngDataIfExists(Buffer.alloc(0)));
+  });
+
+  it('returns null for non-PNG files', async () => {
+    await Promise.all(
+      [
+        'kitten-1-64-64.jpg',
+        '512x515-thumbs-up-lincoln.webp',
+        'giphy-GVNvOUpeYmI7e.gif',
+        'pixabay-Soap-Bubble-7141.mp4',
+        'lorem-ipsum.txt',
+      ].map(async filename => {
+        assert.isNull(getAnimatedPngDataIfExists(await fixture(filename)));
+      })
+    );
+  });
+
+  it('returns null for non-animated PNG files', async () => {
+    assert.isNull(
+      getAnimatedPngDataIfExists(await fixture('20x200-yellow.png'))
+    );
+  });
+
+  it('returns data for animated PNG files', async () => {
+    assert.deepEqual(
+      getAnimatedPngDataIfExists(
+        await fixture('Animated_PNG_example_bouncing_beach_ball.png')
+      ),
+      { numPlays: Infinity }
+    );
+
+    assert.deepEqual(
+      getAnimatedPngDataIfExists(await fixture('apng_with_2_plays.png')),
+      { numPlays: 2 }
+    );
+  });
+});