C#、NUnit : How to deal with testing of exceptions and deferred execution

Question

假设我们有一个看起来像这样的方法:

public IEnumerable<Dog> GrowAll(this IEnumerable<Puppy> puppies)
{
    if(subjects == null)
        throw new ArgumentNullException("subjects");

    foreach(var puppy in puppies)
        yield return puppy.Grow();
}

如果我通过这样做来测试:

Puppy[] puppies = null;
Assert.Throws<ArgumentNullException>(() => puppies.GrowAll());

测试将失败说它

Expected: <System.ArgumentNullException>
But was: null

我可以通过将测试更改为

来解决这个问题

Puppy[] puppies = null;
Assert.Throws<ArgumentNullException>(() => puppies.GrowAll().ToArray());

这就是您通常的做法吗？还是有更好的方法来编写测试？或者也许是编写方法本身的更好方法？

---

尝试对内置 Select 做同样的事情方法，即使没有 ToArray 也失败了或类似的东西，所以显然你可以做些什么......我只是不知道是什么:p

Answer 1

测试没问题 - 你的代码不行。您应该通过将方法分成两半来使代码在调用时立即抛出异常:

public IEnumerable<Dog> GrowAll(this IEnumerable<Puppy> puppies)
{
    if(subjects == null)
        throw new ArgumentNullException("subjects");

    return GrowAllImpl(puppies);
}

private IEnumerable<Dog> GrowAllImpl(this IEnumerable<Puppy> puppies)
{
    foreach(var puppy in puppies)
        yield return puppy.Grow();
}