favicon: Refactor handler and add tests

src/tests/backend/specs/favicon.js

@@ -0,0 +1,55 @@
+'use strict';
+
+const assert = require('assert').strict;
+const common = require('../common');
+const fs = require('fs');
+const fsp = fs.promises;
+const path = require('path');
+const settings = require('../../../node/utils/Settings');
+const superagent = require('superagent');
+
+describe(__filename, function () {
+  let agent;
+  let backupSettings;
+  let skinDir;
+  let wantDefaultIcon;
+  let wantSkinIcon;
+
+  before(async function () {
+    agent = await common.init();
+    wantDefaultIcon = await fsp.readFile(path.join(settings.root, 'src', 'static', 'favicon.ico'));
+    wantSkinIcon = await fsp.readFile(path.join(__dirname, 'favicon-test-skin.png'));
+  });
+
+  beforeEach(async function () {
+    backupSettings = {...settings};
+    skinDir = await fsp.mkdtemp(path.join(settings.root, 'src', 'static', 'skins', 'test-'));
+    settings.skinName = path.basename(skinDir);
+  });
+
+  afterEach(async function () {
+    delete settings.skinName;
+    Object.assign(settings, backupSettings);
+    try {
+      // TODO: The {recursive: true} option wasn't added to fsp.rmdir() until Node.js v12.10.0 so we
+      // can't rely on it until support for Node.js v10 is dropped.
+      await fsp.unlink(path.join(skinDir, 'favicon.ico'));
+      await fsp.rmdir(skinDir, {recursive: true});
+    } catch (err) { /* intentionally ignored */ }
+  });
+
+  it('uses skin favicon if present', async function () {
+    await fsp.writeFile(path.join(skinDir, 'favicon.ico'), wantSkinIcon);
+    const {body: gotIcon} = await agent.get('/favicon.ico')
+        .accept('png').buffer(true).parse(superagent.parse.image)
+        .expect(200);
+    assert(gotIcon.equals(wantSkinIcon));
+  });
+
+  it('falls back to default favicon', async function () {
+    const {body: gotIcon} = await agent.get('/favicon.ico')
+        .accept('png').buffer(true).parse(superagent.parse.image)
+        .expect(200);
+    assert(gotIcon.equals(wantDefaultIcon));
+  });
+});