如何在 NUnit 中模拟 StreamReader答案

【问题标题】：How to mock StreamReader in NUnit如何在 NUnit 中模拟 StreamReader
【发布时间】：2021-11-16 22:44:20
【问题描述】：

我正在尝试使用 NUnit 和 Moq 为我的示例项目编写单元测试。我有如下服务类：

public class SentimentService : ISentimentService
{
    private readonly IStreamReader _reader;
    private readonly IServerClient _serverClient;

    public SentimentService(IStreamReader reader, IServerClient serverClient)
    {
        _reader = reader;
        _serverClient = serverClient;
    }


    public async Task<string> CalculateSentimentFromTextFile(IFormFile file)
    {
        var input = "";
        using (StreamReader streamReader = _reader.GetReader(file.OpenReadStream()))
        {
            input = streamReader.ReadToEnd();
            streamReader.Close();
        }

        var result = await _serverClient.PostAsync<SentimentResult, string>($"submit_string", input);

        return result.label;
    }
}

我尝试使用 Moq，如下所示：

[Test]
public async Task CalculateSentimentFromTextFileEquality()
{
    var mockFormFile = new Mock<IFormFile>();
    var mockStreamReader = new Mock<IStreamReader>();
    var mockServerClient = new Mock<IServerClient>();

    var mockResult = new SentimentResult
    {
        label = "Positive"
    };

    mockStreamReader.Setup(o => o.GetReader(mockFormFile.Object.OpenReadStream()));

    mockServerClient.Setup(o => o.PostAsync<SentimentResult, string>(It.IsAny<string>(), It.IsAny<string>())).ReturnsAsync(mockResult);

    var sut = new SentimentService(mockStreamReader.Object, mockServerClient.Object);
    var result = await sut.CalculateSentimentFromTextFile(mockFormFile.Object);

    Assert.That(result, Is.EqualTo("Positive"));
}

但是，得到以下错误：

【问题讨论】：

能否告诉我们SentimentServiceTest 中的#35 是哪一行？

标签： c# unit-testing nunit asp.net-core-webapi moq

【解决方案1】：

这个设置：

 mockStreamReader.Setup(o => o.GetReader(mockFormFile.Object.OpenReadStream()));

不返回任何对象，因此在 SUT 中调用它时：

StreamReader streamReader = _reader.GetReader(file.OpenReadStream()

将返回一个空对象。

然而，StreamReader 有无参数构造函数，这意味着如果你想模拟它，你必须提供真实的文件路径/流。处理StreamReader 的一种方法是创建一个接口，该接口稍后可以由StreamReader 的包装器实现。

public interface IStreamReader : IDisposable
{
    string ReadToEnd();
    void Close();
}

IStreamReader 的创建是由工厂制造的：

public interface IStreamReaderFactory
{
    IStreamReader GetReader(Stream stream);
}

您的 SUT 可以修改为：

public class SentimentService : ISentimentService
{
    private readonly IStreamReaderFactory _readerFactory;
    private readonly IServerClient _serverClient;

    public SentimentService(IStreamReaderFactory readerFactory, IServerClient serverClient)
    {
        _readerFactory = readerFactory;
        _serverClient = serverClient;
    }


    public async Task<string> CalculateSentimentFromTextFile(IFormFile file)
    {
         var input = "";
         using (IStreamReader streamReader = _readerFactory.GetReader(file.OpenReadStream()))
         {
             input = streamReader.ReadToEnd();
             streamReader.Close();
         }

         var result = await _serverClient.PostAsync<SentimentResult, string>($"submit_string", input);

         return result.label;
    }
}

测试代码现在应该能够正确设置IStreamReader。

var mockStreamReader = new Mock<IStreamReader>();
var mockStreamReaderFactory = new Mock<IStreamReaderFactory>();

mockStreamReaderFactory.Setup(o => o.GetReader(It.IsAny<Stream>())).Returns(mockStreamReader.Object);

【讨论】：