test(responseInterceptor): add unit test

test/unit/response-interceptor.spec.ts

@@ -0,0 +1,63 @@
+import { IncomingMessage, ServerResponse } from 'http';
+
+import { responseInterceptor } from '../../src/handlers/response-interceptor';
+
+const fakeProxyResponse = () => {
+  const httpIncomingMessage = new IncomingMessage(null);
+  httpIncomingMessage._read = () => ({});
+  return httpIncomingMessage;
+};
+
+const fakeResponse = () => {
+  const httpIncomingMessage = fakeProxyResponse();
+
+  const response = new ServerResponse(httpIncomingMessage);
+  response.setHeader = jest.fn();
+  response.write = jest.fn();
+  response.end = jest.fn();
+
+  return response;
+};
+
+const waitInterceptorHandler = (ms = 1): Promise<void> =>
+  new Promise((resolve) => setTimeout(resolve, ms));
+
+describe('responseInterceptor', () => {
+  it('should write body on end proxy event', async () => {
+    const httpIncomingMessage = fakeProxyResponse();
+    const response = fakeResponse();
+
+    responseInterceptor(async () => JSON.stringify({ someField: '' }))(
+      httpIncomingMessage,
+      null,
+      response
+    );
+
+    httpIncomingMessage.emit('end');
+    await waitInterceptorHandler();
+
+    const expectedBody = JSON.stringify({ someField: '' });
+    expect(response.setHeader).toHaveBeenCalledWith('content-length', expectedBody.length);
+    expect(response.write).toHaveBeenCalledWith(Buffer.from(expectedBody));
+    expect(response.end).toHaveBeenCalledWith();
+  });
+
+  it('should end with error when receive a proxy error event', async () => {
+    const httpIncomingMessage = fakeProxyResponse();
+    const response = fakeResponse();
+
+    responseInterceptor(async () => JSON.stringify({ someField: '' }))(
+      httpIncomingMessage,
+      null,
+      response
+    );
+
+    httpIncomingMessage.emit('error', new Error('some error meessage'));
+
+    expect(response.setHeader).not.toHaveBeenCalled();
+    expect(response.write).not.toHaveBeenCalled();
+    expect(response.end).toHaveBeenCalledWith(
+      'Error fetching proxied request: some error meessage'
+    );
+  });
+});