xUnit 对 Json 文件进行读写测试

Question

我正在 NancyFx 中创建一个新应用程序，并且我正在尝试进行测试驱动开发 (TDD) 所以我想要开发的第一个功能是读取和写入 json 文件。现在我知道这很难做到，因为它涉及httpContext，除非应用程序正在运行，否则我显然无法做到。

我想做的是模拟这个，这样我就可以创建一个用于读取和写入 json 文件的单元测试。谁能给我举个例子来说明我如何做到这一点并解释你是如何做到的？

我有两种方法，一种是阅读，一种是写作，如下所示：

ReadToJsonFile 方法：

public IEnumerable<T> ReadFile<T>(string fileName)
    {
        try
        {
            var readFile = File.ReadAllText(HttpContext.Current.Server.MapPath(fileName));
            var list = JsonConvert.DeserializeObject<List<T>>(readFile);
            return list;
        }
        catch (Exception ex)
        {
            _logger.LogException(ex);
            return null;
        }
    }

WriteToJsonFile 方法：

public bool WriteFile<T>(string fileName, IEnumerable<T> list)
    {
        try
        {
            var listContent = JsonConvert.SerializeObject(list, Formatting.Indented);
            File.WriteAllText(HttpContext.Current.Server.MapPath(fileName), listContent);
            return true;
        }
        catch (Exception ex)
        {
            _logger.LogException(ex);
            return false;
        }
    }

任何建议都会很棒，谢谢。

Answer 1

我建议您使用适配器或外观来抽象出使用 System.IO 静态方法：

public class JsonWriter
{
    private readonly IFileSystem _file;
    private readonly HttpContextBase _httpContext;
    private readonly ILog _logger;

    public JsonWriter(
        IFileSystem file, 
        HttpContextBase httpContext,
        ILog logger)
    {
        _file = file;
        _httpContext = httpContext;
        _logger = logger;
    }

    public bool WriteFile<T>(string fileName, IEnumerable<T> list)
    {
        try
        {
            var listContent = JsonConvert.SerializeObject(list, Formatting.Indented);
            _file.WriteAllText(_httpContext.Server.MapPath(fileName), listContent);
            return true;
        }
        catch (Exception ex)
        {
            _logger.LogException(ex);
            return false;
        }
    }

}

你需要这样的界面：

///<summary>Implementors are wrappers for static methods of System.IO.File and System.IO.Directory
///</summary>
public interface IFileSystem
{

    ///<summary>Creates a new file, writes the specified string to the file, then closes the file. If the file already exists, it is overwritten.
    ///</summary>
    ///<param name="path">The file to write to</param>
    ///<param name="contents">The string to write to the file</param>
    void WriteAllText(string path, string contents);

    ///<summary>Creates a new file, writes the specified string to the file, then closes the file. If the file already exists, it is overwritten.
    ///</summary>
    ///<param name="path">The file to write to</param>
    ///<param name="contents">The string to write to the file</param>
    ///<param name="encoding">An <see cref="Encoding"/> object that represents the encoding to apply to the string</param>
    void WriteAllText(string path, string contents, Encoding encoding);

}

还有这样的实现：

///<summary>Replaces the static methods of System.IO.File
///</summary>
public class FileSystem : IFileSystem
{
    ///<summary>Creates a new file, writes the specified string to the file, then closes the file. If the file already exists, it is overwritten.
    ///</summary>
    ///<param name="path">The file to write to</param>
    ///<param name="contents">The string to write to the file</param>
    public void WriteAllText(string path, string contents)
    {
        File.WriteAllText(path, contents);
    }

    ///<summary>Creates a new file, writes the specified string to the file, then closes the file. If the file already exists, it is overwritten.
    ///</summary>
    ///<param name="path">The file to write to</param>
    ///<param name="contents">The string to write to the file</param>
    ///<param name="encoding">An <see cref="Encoding"/> object that represents the encoding to apply to the string</param>
    public void WriteAllText(string path, string contents, Encoding encoding)
    {
        File.WriteAllText(path, contents, encoding);
    }
}

现在您可以在单元测试中模拟文件方法和 HttpContext。