如何使用NUnit在C#中对线程安全通用列表进行单元测试？

我问了一个关于构建自定义Thread Safe Generic List的问题,现在我正在尝试进行单元测试,我完全不知道如何做到这一点.由于锁定发生在ThreadSafeList类中,我不确定如何在我尝试模仿多个add调用时使列表锁定一段时间.谢谢.

Can_add_one_item_at_a_time

[Test]
public void Can_add_one_item_at_a_time() //this test won't pass
{
    //I am not sure how to do this test...
    var list = new ThreadSafeList<string>();

    //some how need to call lock and sleep inside list instance
    //say somehow list locks for 1 sec

    var ta = new Thread(x => list.Add("a"));
    ta.Start(); //does it need to aboard say before 1 sec if locked

    var tb = new Thread(x => list.Add("b"));
    tb.Start(); //does it need to aboard say before 1 sec if locked

    //it involves using GetSnapshot()
    //which is bad idea for unit testing I think
    var snapshot = list.GetSnapshot(); 
    Assert.IsFalse(snapshot.Contains("a"), "Should not contain a.");
    Assert.IsFalse(snapshot.Contains("b"), "Should not contain b.");
}

Snapshot_should_be_point_of_time_only

[Test]
public void Snapshot_should_be_point_of_time_only()
{
    var list = new ThreadSafeList<string>();
    var ta = new Thread(x => list.Add("a"));
    ta.Start();

    ta.Join();
    var snapshot = list.GetSnapshot();

    var tb = new Thread(x => list.Add("b"));
    tb.Start();

    var tc = new Thread(x => list.Add("c"));
    tc.Start();

    tb.Join();
    tc.Join();

    Assert.IsTrue(snapshot.Count == 1, "Snapshot should only contain 1 item.");
    Assert.IsFalse(snapshot.Contains("b"), "Should not contain a.");
    Assert.IsFalse(snapshot.Contains("c"), "Should not contain b.");
}

实例方法

public ThreadSafeList<T> Instance<T>()
{
    return new ThreadSafeList<T>();
}

解决方法:

让我们来看看你的第一个测试,Can_add_one_item_at_a_time.

首先,你的退出条件没有意义.两个项目都应该添加,一次只添加一个.所以当然你的测试会失败.

您也不需要制作快照;记住,这是一个测试,当你的测试运行时,没有别的东西会触及列表.

最后但同样重要的是,您需要确保在所有线程实际完成之前,您不会尝试评估退出条件.最简单的方法是使用计数器和等待事件.这是一个例子：

[Test]
public void Can_add_from_multiple_threads()
{
    const int MaxWorkers = 10;

    var list = new ThreadSafeList<int>(MaxWorkers);
    int remainingWorkers = MaxWorkers;
    var workCompletedEvent = new ManualResetEvent(false);
    for (int i = 0; i < MaxWorkers; i++)
    {
        int workerNum = i;  // Make a copy of local variable for next thread
        ThreadPool.QueueUserWorkItem(s =>
        {
            list.Add(workerNum);
            if (Interlocked.Decrement(ref remainingWorkers) == 0)
                workCompletedEvent.Set();
        });
    }
    workCompletedEvent.WaitOne();
    workCompletedEvent.Close();
    for (int i = 0; i < MaxWorkers; i++)
    {
        Assert.IsTrue(list.Contains(i), "Element was not added");
    }
    Assert.AreEqual(MaxWorkers, list.Count,
        "List count does not match worker count.");
}

现在这确实带来了Add发生的可能性,以至于没有两个线程会同时尝试执行它. No Refunds No Returns部分解释了如何插入条件延迟.我实际上会定义一个特殊的测试标志,而不是DEBUG.在构建配置中,添加一个名为TEST的标志,然后将其添加到ThreadSafeList类：

public class ThreadSafeList<T>
{
    // snip fields

    public void Add(T item)
    {
        lock (sync)
        {
            TestUtil.WaitStandardThreadDelay();
            innerList.Add(item);
        }
    }

    // snip other methods/properties
}

static class TestUtil
{
    [Conditional("TEST")]
    public static void WaitStandardThreadDelay()
    {
        Thread.Sleep(1000);
    }
}

只要构建配置定义了TEST标志,这将导致Add方法在实际添加项目之前等待1秒.整个测试至少需要10秒钟;如果它完成得比这更快,那就错了.

考虑到这一点,我将把第二次测试留给你.它很相似.

标签：c,unit-testing,multithreading,thread-safety,generic-list
来源： https://codeday.me/bug/20190610/1213782.html