public void RetryAsyncFunction()
        {
            // Arrange && Act.
            var result = Retrier.Init()
                         .Invoke(async() => await FakeService.GetHelloWorldAsync());

            // Assert.
            Assert.Equal("Hello world", result.Result.Result);
            Assert.Equal(1, result.RetryInfo.Executions);
            Assert.True(result.Successful);
        }