Hard to test

Context: async void methods are difficult to unit test because there is no Task to await. You cannot know when the method completes or whether it threw an exception.

using System.Threading.Tasks;
using Xunit;

public class MyService
{
    // Bad: cannot be tested easily
    public async void DoAsyncVoid()
    {
        await Task.Delay(10);
    }

    // Good: returns Task
    public async Task DoAsyncTask()
    {
        await Task.Delay(10);
    }
}

public class MyServiceTests
{
    [Fact]
    public async Task TestAsyncVoid_Problem()
    {
        var service = new MyService();
        service.DoAsyncVoid(); // cannot await, cannot verify completion
        // You would need to add arbitrary delays...
        await Task.Delay(100); // fragile test
    }

    [Fact]
    public async Task TestAsyncTask_Good()
    {
        var service = new MyService();
        await service.DoAsyncTask(); // can await, test is reliable
    }
}

Solution

Change the method to return Task.

Real-world usage example

Unit testing with xUnit: xUnit does not support async void tests; they must return Task.

Example: xUnit async tests

Hard to test

Solution

Real-world usage example

Related sections