message: refactor: use prototype to access private properties and avoid //
diff: @@ -36,8 +36,15 @@ describe('ServiceBuilderImpl', () => {
  });
  describe('setCustomErrorHandler', () => {
  + it('check if custom error handler is undefined', () => {
  + const serviceBuilder = new ServiceBuilderImpl(module);
  + const serviceBuilderProto = Object.getPrototypeOf(serviceBuilder);
  + expect(serviceBuilderProto.errorHandler).toBeUndefined();
  + });
  +
  it('adds custom error handler', () => {
  const serviceBuilder = new ServiceBuilderImpl(module);
  + const serviceBuilderProto = Object.getPrototypeOf(serviceBuilder);
  const customErrorHandler = (
  error: Error,
  _req: Request,
  @@ -46,12 +53,8 @@ describe('ServiceBuilderImpl', () => {
  ) => {
  next(error);
  };
  - serviceBuilder.setErrorHandler(customErrorHandler);
  - expect(serviceBuilder.errorHandler).toEqual(customErrorHandler);
  - });
  - it('use default error handler', () => {
  - const serviceBuilder = new ServiceBuilderImpl(module);
  - expect(serviceBuilder.errorHandler).toBeUndefined();
  + serviceBuilderProto.setErrorHandler(customErrorHandler);
  + expect(serviceBuilderProto.errorHandler).toEqual(customErrorHandler);
  });
  });
  });
  