使用 AutoFixture 创建递归树 [英] Creating recursive tree with AutoFixture
问题描述
我刚刚开始使用 AutoFixture 并拥有这个半复杂的数据结构，我想为其创建一些样本.在我正在使用的测试中，我不太关心数据结构的内容.我只想要合理的默认值.
I have just started using AutoFixture and have this semi-complex data structure that I would like to create some specimen for. In the tests I am working with I don't care too much about content of the data structure. I just want reasonable default values.
这个数据结构的一部分是递归树.更具体地说，一个类包含其他一些类的集合，其中包含其自身的子项列表.类似于:
Part of this data structure is a recursive tree. More specific, one class holds a collection of some other class that contains a list of children of itself. Something akin to:
public class A
{
private IEnumerable<B> bNodes;
public A(IEnumerable<B> bNodes)
{
this.bNodes = bNodes;
}
}
public class B
{
private IEnumerable<B> children;
public B(IEnumerable<B> children)
{
this.children = children;
}
}
假设由于各种原因我不能轻易改变这个结构.
Lets assume I cannot easily change this structure for various reasons.
如果我让我的装置创建 A ThrowingRecursionBehavior 将开始吠叫 B 是递归的.
If I ask my fixture to create A ThrowingRecursionBehavior will start barking about B being recursive.
如果我用 OmitOnRecursionBehavior 替换 ThrowingRecursionBehavior，我会得到一个 ObjectCreateException.
If I replace ThrowingRecursionBehavior with OmitOnRecursionBehavior I get an ObjectCreateException.
如果我尝试类似:fixture.Inject(Enumerable.Empty());我从 DictionaryFiller 收到已添加具有相同键的项目".如果我用 NullRecursionBehavior 替换 ThrowingRecursionBehavior，也会发生同样的事情.
If I try something like: fixture.Inject(Enumerable.Empty()); I get "An item with the same key has already been added" from the DictionaryFiller. The same thing happens if I replace ThrowingRecursionBehavior with NullRecursionBehavior.
有几件事我想要.
- 用空的 B 列表创建 A 的样本的最佳方法是什么?
- 创建带有几个 B 的 A 样本的最佳方法是什么，该样本包含几个 B-孩子和几个孩子(一棵小树)?
对于我的最后一个愿望，在使用 Enumerable.Empty(或零大小的数组/列表或什至 null)之后指定一些递归深度可能会很好.我知道 AutoFixture 的扩展非常灵活.所以我想应该可以创建一些完全做到这一点的样本构建器.事实上，我会尝试使用自定义的 ISpecimenBuilder，但也许有人已经有了更聪明的解决方案.例如，在 RecursionGuard 中修改这一行是否有意义:
For my last wish it could be nice to specify some recursion depth after which Enumerable.Empty was used (or a zero sized array / List or even null). I know that AutoFixture is very flexible to extend. So I suppose it should be possible to create some specimen builder that does exactly this. In fact I will try fooling around with a custom ISpecimenBuilder, but perhaps someone has a smarter solution already. For example, would it make sense to modify this line in RecursionGuard:
public object Create(object request, ISpecimenContext context)
{
if (this.monitoredRequests.Any(x => this.comparer.Equals(x, request)))
...
到
public object Create(object request, ISpecimenContext context)
{
if (this.monitoredRequests.Count(x => this.comparer.Equals(x, request)) > maxAllowedRecursions)
...
推荐答案
用空的 B 列表创建 A
使用空的 B 列表创建 A 的实例很容易:
It's easy to create an instance of A with an empty list of Bs:
var fixture = new Fixture();
fixture.Inject(Enumerable.Empty<B>());
var a = fixture.Create<A>();
创建一棵小树
创建一棵小树要困难得多，但它是可能的.您对 RecursionGuard 的思考已经步入正轨.为了验证这是否可行，我从 RecursionGuard 复制了大部分代码并创建了这个 DepthRecursionGuard 作为概念证明:>
It's much more difficult to create a small tree, but it's possible. You're already on track with your thinking about RecursionGuard. In order to verify if this could work, I copied most of the code from RecursionGuard and created this DepthRecursionGuard as a proof of concept:
public class DepthRecursionGuard : ISpecimenBuilderNode
{
private readonly ISpecimenBuilder builder;
private readonly Stack<object> monitoredRequests;
public DepthRecursionGuard(ISpecimenBuilder builder)
{
if (builder == null)
{
throw new ArgumentNullException("builder");
}
this.monitoredRequests = new Stack<object>();
this.builder = builder;
}
public object Create(object request, ISpecimenContext context)
{
if (this.monitoredRequests.Count(request.Equals) > 1)
return this.HandleRecursiveRequest(request);
this.monitoredRequests.Push(request);
var specimen = this.builder.Create(request, context);
this.monitoredRequests.Pop();
return specimen;
}
private object HandleRecursiveRequest(object request)
{
if (typeof(IEnumerable<B>).Equals(request))
return Enumerable.Empty<B>();
throw new InvalidOperationException("boo hiss!");
}
public ISpecimenBuilderNode Compose(IEnumerable<ISpecimenBuilder> builders)
{
var builder = ComposeIfMultiple(builders);
return new DepthRecursionGuard(builder);
}
public virtual IEnumerator<ISpecimenBuilder> GetEnumerator()
{
yield return this.builder;
}
IEnumerator IEnumerable.GetEnumerator()
{
return this.GetEnumerator();
}
private static ISpecimenBuilder ComposeIfMultiple(
IEnumerable<ISpecimenBuilder> builders)
{
var isSingle = builders.Take(2).Count() == 1;
if (isSingle)
return builders.Single();
return new CompositeSpecimenBuilder(builders);
}
}
注意Create方法的改变实现，以及HandleRecursiveRequest中IEnumerable的具体处理.
Notice the changed implementation of the Create method, as well as the specific handling of IEnumerable<B> in HandleRecursiveRequest.
为了让 Fixture 实例可用，我还添加了这个 DepthRecursionBehavior:
In order to make this usable from a Fixture instance, I also added this DepthRecursionBehavior:
public class DepthRecursionBehavior : ISpecimenBuilderTransformation
{
public ISpecimenBuilder Transform(ISpecimenBuilder builder)
{
return new DepthRecursionGuard(builder);
}
}
这使我能够创建一棵小树:
This enabled me to create a small tree:
var fixture = new Fixture();
fixture.Behaviors.OfType<ThrowingRecursionBehavior>()
.ToList().ForEach(b => fixture.Behaviors.Remove(b));
fixture.Behaviors.Add(new DepthRecursionBehavior());
var a = fixture.Create<A>();
虽然这是可能的，但在我看来，这太难了，所以我创建了 a工作项，以便将来更轻松.
While this is possible, it's, in my opinion, too hard, so I've created a work item to make it easier in the future.
更新 2013.11.13:从 AutoFixture 3.13.0 开始，可以通过该 API 配置递归深度.
Update 2013.11.13: From AutoFixture 3.13.0, the recursion depth can be configured via that API.
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