Integration Testing multipart/form-data c#

Question

I have trouble trying to create an integration test for my post call that accepts a viewmodel that has amongst other values, an IFormFile, which makes this call from an application/json to a multipart/form-data

My IntegrationSetup class

protected static IFormFile GetFormFile()
        {
            byte[] bytes = Encoding.UTF8.GetBytes("test;test;");

            var file = new FormFile(
                baseStream: new MemoryStream(bytes),
                baseStreamOffset: 0,
                length: bytes.Length,
                name: "Data",
                fileName: "dummy.csv"
            )
            {
                Headers = new HeaderDictionary(),
                ContentType = "text/csv"
            };

            return file;
        } 

My Test Method

public async Task CreateAsync_ShouldReturnId()
        {
            //Arrange
            using var content = new MultipartFormDataContent();
            var stringContent = new StringContent(
                JsonConvert.SerializeObject(new CreateArticleViewmodel
                {
                    Title = "viewModel.Title",
                    SmallParagraph = "viewModel.SmallParagraph",
                    Url = "viewModel.Url",
                    Image = GetFormFile()
                }),
                Encoding.UTF8,
                "application/json");
            stringContent.Headers.Add("Content-Disposition", "form-data; name=\"json\"");
            content.Add(stringContent, "json");

            //Act
            var response = await httpClient.PostAsync($"{Url}", content);
            //Assert
            response.StatusCode.ShouldBe(HttpStatusCode.OK);
            int id = int.Parse(await response.Content.ReadAsStringAsync());
            id.ShouldBeGreaterThan(0);
        }

My Controller Method

[HttpPost]
        public async Task<IActionResult> CreateArticleAsync([FromForm] CreateArticleViewmodel viewModel)
        {

            var id = await _service.CreateAsync(viewModel).ConfigureAwait(false);
            if (id > 0)
                return Ok(id);
            return BadRequest();
        }

It throws a BadRequest without getting inside the method.

Answer 1

The way you are posting the request contents to the API, in your code, is not correct.

When the API expects a FileInfo in the request payload, posting JSON content never works. You need to send the payload as MultipartFormData and not as JSON.

Consider following example.

This is a an API endpoint which expects and model with FileInfo in it as payload.

[HttpPost]
public IActionResult Upload([FromForm] MyData myData)
{
    if (myData.File != null)
    {
        return Ok("File received");
    }
    else
    {
        return BadRequest("File no provided");
    }
}

public class MyData
{
    public int Id { get; set; }
    public string Title { get; set; }
    // Below property is used for getting file from client to the server.
    public IFormFile File { get; set; }
}

This is pretty much the same API as yours.

Following is the client code which calls the above API with file and other model properties.

var apiURL = "http://localhost:50492/home/upload";
const string filename = "D:\\samplefile.docx";

HttpClient _client = new HttpClient();

// Instead of JSON body, multipart form data will be sent as request body.
var httpContent = new MultipartFormDataContent();
var fileContent = new ByteArrayContent(File.ReadAllBytes(filename));
fileContent.Headers.ContentType = MediaTypeHeaderValue.Parse("multipart/form-data");

// Add File property with file content
httpContent.Add(fileContent, "file", filename);

// Add id property with its value
httpContent.Add(new StringContent("789"), "id");

// Add title property with its value.
httpContent.Add(new StringContent("Some title value"), "title");

// send POST request.
var response = await _client.PostAsync(apiURL, httpContent);
response.EnsureSuccessStatusCode();
var responseContent = await response.Content.ReadAsStringAsync();

// output the response content to the console.
Console.WriteLine(responseContent);

The client code is running from a Console application. So when I run this, the expectation is to get File received message in the console and I am getting that message.

Following is the screen capture of the model content at the API end while debugging it.

And if I am calling this API from postman, it would look like following.

I hope this will help you solve your issue.