How to get argument exeption response from value task method by Assert.ThrowsAsync?-CodePudding

My service class methode is

public async ValueTask<HttpResponseMessage> UploadFileAsync(string fileKey)
{
  ..
  var multipartContent = new MultipartFormDataContent();
  multipartContent.Add(httpContent, "upfile", Path.GetFileName(fileKey));
  //in negative test case I am sending empty fileKey value then throwing argument exception from here
  ..
  return httpResponseMessage;
}

I am calling this value task fileupload method in my test case like below

[Fact]
public async Task UploadFileAsync_WhenFileKeyParameterIsEmpty_ReturnArguementException()
{
     string fileKey = "";
     var ex = Assert.Throws<ArgumentException>(()=>objHttpService.UploadFileAsync(fileKey)); 
     Assert.Equal("The value cannot be null or empty. (Parameter 'fileName')", ex.Message);
}

I couldn't able to get any response in ex variable, and getting assert failure like below.

Message: Assert.Throws() Failure Expected: typeof(System.ArgumentException) Actual: (No exception was thrown)

CodePudding user response：

var ex = await Assert.ThrowsAsync<ArgumentException>(
    () => objHttpService.UploadFileAsync(fileKey));

The Throws version would only detect problems if the async API threw synchronously, rather than the more typical behaviour of synchronously or asynchronously returning a faulted value-task.

CodePudding user response：

You have two issues. Firstly because your code is async you need to use xUnit's ThrowsAsync method and await the result.

Secondly ThrowsAsync expects a Func<Task> as a parameter, and () => UploadFileAsync(fileKey) is a Func<ValueTask>. We can get around this by calling AsTask() on the result of the call to UploadFileAsync. So we need to change the call to Assert.Throws to:

var ex = await Assert.ThrowsAsync<ArgumentException>(
    () => objHttpService.UploadFileAsync(fileKey).AsTask());

Working test code is below. Note that UploadFileAsync is just a test stub that should behave like the method you are testing.

public class objHttpService
{
    [Fact]
    public async Task UploadFileAsync_WhenFileKeyParameterIsEmpty_ReturnArguementException()
    {
        string fileKey = "";
        var ex = await Assert.ThrowsAsync<ArgumentException>(
            () => objHttpService.UploadFileAsync(fileKey).AsTask());
        Assert.Equal("The value cannot be null or empty. (Parameter 'fileName')", ex.Message);
    }

    // Test code only - existing method shouldn't need to be changed
    public static async ValueTask<HttpResponseMessage> UploadFileAsync(string _)
    {
        await Task.Delay(10);
        throw new ArgumentException("The value cannot be null or empty. (Parameter 'fileName')");
    }
}