如何使用ModelMetadata模拟NSubstitute类？

Question

在我的图书馆里，我有一个简单的课程：

public class FormDataJsonBinderProvider : IModelBinderProvider 
{
    // code ommited

    public IModelBinder GetBinder(ModelBinderProviderContext context)
    {
        // some logic
    }
}

我想测试它，但要做到这一点，我必须以某种方式模拟ModelMetadata(context.Metadata是ModelMetadata类型)，这是一个具有该签名的abstract类：

public abstract class ModelMetadata : IEquatable<ModelMetadata?>, IModelMetadataProvider 
{
    // some props and methods

    internal virtual bool PropertyHasValidators => false; // problematic property :(
}

在我的测试中

[Test]
public void GetBinder_SimpleType_ShouldThrowException() 
{
    // Arrange
    var metadata = Substitute.For<ModelMetadata>();
    metadata.IsComplexType.Returns(false);
}

我得到了System.ArgumentException : Can not instantiate proxy of class: Microsoft.AspNetCore.Mvc.ModelBinding.ModelMetadata. Could not find a parameterless constructor. (Parameter 'constructorArguments')，这是完全公平的。

所以。我做了一个TestModelMetadata类：

public abstract class TestModelMetadata : ModelMetadata {
    public TestModelMetadata() : base(new ModelMetadataIdentity()) { }

    public new virtual bool IsComplexType { get; }

    public override IReadOnlyDictionary<object, object> AdditionalValues { get; }
    // More overridden props
}

我就是这样用的：

public void GetBinder_SimpleType_ShouldThrowException() 
{
    // Arrange
    var metadata = Substitute.For<TestModelMetadata>();
    metadata.IsComplexType.Returns(false);
}

在这里我得到一个奇怪的例外：

System.TypeLoadException : Method 'get_PropertyHasValidators' on type 'Castle.Proxies.TestModelMetadataProxy' from assembly 'DynamicProxyGenAssembly2, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null' is overriding a method that is not visible from that assembly.
   at System.Reflection.Emit.TypeBuilder.CreateTypeNoLock()
   at System.Reflection.Emit.TypeBuilder.CreateTypeInfo()
   at Castle.DynamicProxy.Generators.Emitters.AbstractTypeEmitter.BuildType()
   at Castle.DynamicProxy.Generators.BaseClassProxyGenerator.GenerateType(String name, INamingScope namingScope)
   at Castle.DynamicProxy.Generators.BaseProxyGenerator.<>c__DisplayClass13_0.<GetProxyType>b__0(CacheKey cacheKey)
   at Castle.Core.Internal.SynchronizedDictionary`2.GetOrAdd(TKey key, Func`2 valueFactory)
   at Castle.DynamicProxy.Generators.BaseProxyGenerator.GetProxyType()
   at Castle.DynamicProxy.DefaultProxyBuilder.CreateClassProxyType(Type classToProxy, Type[] additionalInterfacesToProxy, ProxyGenerationOptions options)
   at Castle.DynamicProxy.ProxyGenerator.CreateClassProxyType(Type classToProxy, Type[] additionalInterfacesToProxy, ProxyGenerationOptions options)
   at Castle.DynamicProxy.ProxyGenerator.CreateClassProxy(Type classToProxy, Type[] additionalInterfacesToProxy, ProxyGenerationOptions options, Object[] constructorArguments, IInterceptor[] interceptors)
   at NSubstitute.Proxies.CastleDynamicProxy.CastleDynamicProxyFactory.CreateProxyUsingCastleProxyGenerator(Type typeToProxy, Type[] additionalInterfaces, Object[] constructorArguments, IInterceptor[] interceptors, ProxyGenerationOptions proxyGenerationOptions)
   at NSubstitute.Proxies.CastleDynamicProxy.CastleDynamicProxyFactory.GenerateTypeProxy(ICallRouter callRouter, Type typeToProxy, Type[] additionalInterfaces, Object[] constructorArguments)
   at NSubstitute.Proxies.CastleDynamicProxy.CastleDynamicProxyFactory.GenerateProxy(ICallRouter callRouter, Type typeToProxy, Type[] additionalInterfaces, Object[] constructorArguments)
   at NSubstitute.Core.SubstituteFactory.Create(Type[] typesToProxy, Object[] constructorArguments, Boolean callBaseByDefault)
   at NSubstitute.Core.SubstituteFactory.Create(Type[] typesToProxy, Object[] constructorArguments)
   at NSubstitute.Substitute.For(Type[] typesToProxy, Object[] constructorArguments)
   at NSubstitute.Substitute.For[T](Object[] constructorArguments)

所以问题是：

如何模拟ModelMetadata类以在测试中使用？

Answer 1

与其仅为测试创建一个TestModelMetadata类，不如告诉NSubstitute在ModelMetadata上使用一个现有的构造函数，如下所示：

[Test]
public void GetBinder_SimpleType_ShouldThrowException() 
{
    // Arrange
    var metadata = Substitute.For<ModelMetadata>(new ModelMetadataIdentity());
    metadata.IsComplexType.Returns(false);
}