runMiddleware.js

  function runMiddleware(middleware, req, res) {
    return new Promise((resolve, reject) => {
      function next(value) {
        if (value instanceof Error) {
          reject(value);
        } else {
          resolve(value);
        }
      }
      middleware(req, res, next);
    });
  }


// in tests
await runMiddleware(myMiddleware, reqMock, resMock);