C#•3y ago

Mocking FileStream for integration testing

I made a simple integration test that tests some functionality after calling an API endpoint. In my api client, I have this function UploadDocumentAsync(string filePath)

public async Task<RestResponse<int>> UploadDocumentAsync(string filePath)
{
    using var formData = new MultipartFormDataContent();

    var fileStream = new StreamContent(new FileStream(filePath));
    var fileName = Path.GetFileName(filePath);
        
    // ...
}

public async Task<RestResponse<int>> UploadDocumentAsync(string filePath)
{
    using var formData = new MultipartFormDataContent();

    var fileStream = new StreamContent(new FileStream(filePath));
    var fileName = Path.GetFileName(filePath);
        
    // ...
}

As you can see, this function expects a string as an argument. To make the function testable though, I'd need an abstraction for FileStream (which I know exists as a NuGet package) and inject it into the function. The question is: Is that better? I know it doesn't sound too bad, but calling the function with a FileStream instead of a string takes away a bit of comfort imo. I don't know if that's just silly goblinresHide

. Or maybe you guys know another way to test such a function

6 Replies

cap5lut•3y ago

i think the simplest way would be to just create a temp file with the desired content and pass its path to the method

HimmDawgOP•3y ago

Hmmm, in that case I should just create some random bytes as data and pass that. I don't wanna bother whether the file was really created etc 😄

cap5lut•3y ago

well, the only other way i can think of would be creating a public async Task<RestResponse<int>> UploadDocumentAsync(string fileName, Stream stream); that does the actual work and which is called by ur current implementation. then u could use for example a MemoryStream instead of a real file

HimmDawgOP•3y ago

Right, I fiddled around a bit and just used System.IO.Abstractions and System.IO.Abstractions.TestingHelpers I injected an IFileSystem into my ApiClient

public ApiClient(HttpClient client, IFileSystem fileSystem)
{
    _client = client;
    _fileSystem = fileSystem;
}

public ApiClient(HttpClient client, IFileSystem fileSystem)
{
    _client = client;
    _fileSystem = fileSystem;
}

and changed the method to

public async Task<RestResponse<int>> UploadDocumentAsync(string filePath)
{
    using var formData = new MultipartFormDataContent();

    var fileStream = new StreamContent(_fileSystem.File.OpenRead(filePath));
    var fileName = Path.GetFileName(filePath);
        
    // ...
}

public async Task<RestResponse<int>> UploadDocumentAsync(string filePath)
{
    using var formData = new MultipartFormDataContent();

    var fileStream = new StreamContent(_fileSystem.File.OpenRead(filePath));
    var fileName = Path.GetFileName(filePath);
        
    // ...
}

And in my test, I created a MockFileSystem which implements IMockFileDataAccessor, which implements IFileSystem

// Arrange
string fakePath = "HelloWorld.txt";
byte[] fakeContent = Encoding.UTF8.GetBytes("Fake file content");

MockFileSystem mockFileSystem = new MockFileSystem();
mockFileSystem.AddFile(fakePath, new MockFileData(fakeContent));

_sut = new ApiClient(client, mockFileSystem);

// Act
var response = await _sut.UploadDocumentAsync(fakePath);

// Arrange
string fakePath = "HelloWorld.txt";
byte[] fakeContent = Encoding.UTF8.GetBytes("Fake file content");

MockFileSystem mockFileSystem = new MockFileSystem();
mockFileSystem.AddFile(fakePath, new MockFileData(fakeContent));

_sut = new ApiClient(client, mockFileSystem);

// Act
var response = await _sut.UploadDocumentAsync(fakePath);

Just if somebody has a similar issue foxNosy

MODiX•3y ago

That command had an error

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HimmDawgOP•3y ago

oh well ¯\_(ツ)_/¯

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Mocking FileStream for integration testing