如何对使用等待延迟的方法进行单元测试

Question

I have created dummy code to describe my issue as follows:

  public class ItemGenerator
    {
        public bool isStopped;
        public List<int> list = new List<int>();
        public void GetItems(int itemsPerSecond)
        {
            int i = 0;
            while (!isStopped)
            {
                list.add(i);
                await Task.Delay(1000);
                i++;
            }
        }
    }



    [Test]
    public void TestGetItmes()
    {
        ItemGenerator gen = new ItemGenerator();

        gen.GetItems(1000);

        await  Task.Delay(5000).ContinueWith(t =>
        {
            gen.isStopped = true;
            Assert.True(gen.list.Count() == (5 * 1000));
        });
    }

Now the problem is that the assert will fail sporadically, I guess it's to do with CPU performance and the fact that there is no guarantee that delay of 1000 will be always 1000ms but what would be the best approach to UT this kind of logic ?

Answer 1

Here's how I would approach this - firstly use the built in CancellationToken

public class ItemGenerator
{
    public List<int> List { get; } = new List<int>();

    public async Task GetItems(CancellationToken token)
    {
        int i = 0;
        while(!token.IsCancellationRequested)
        {
            List.Add(i);
            await Task.Delay(1000);
            i++;
        }
    }
}

Then your test can make use of CancellationTokenSource and specifically CancelAfter method:

var gen = new ItemGenerator();

CancellationTokenSource src = new CancellationTokenSource();
src.CancelAfter(5000);
await gen.GetItems(src.Token);

Note you could pass the CancellationToken in to the constructor of ItemGenerator instead of the method if that is more appropriate.