refactor: Separate middleware from Express.

test/unit/server/middleware/HeaderHandler.test.ts

@@ -0,0 +1,20 @@
+import { createRequest, createResponse } from 'node-mocks-http';
+import { HeaderHandler } from '../../../../src/server/middleware/HeaderHandler';
+import { guardStream } from '../../../../src/util/GuardedStream';
+
+describe('a HeaderHandler', (): void => {
+  let handler: HeaderHandler;
+
+  beforeAll(async(): Promise<void> => {
+    handler = new HeaderHandler();
+  });
+
+  it('returns an X-Powered-By header.', async(): Promise<void> => {
+    const request = guardStream(createRequest());
+    const response = createResponse();
+    await handler.handleSafe({ request, response });
+    expect(response.getHeaders()).toEqual(expect.objectContaining({
+      'x-powered-by': 'Community Solid Server',
+    }));
+  });
+});