Select a specific constructor using AutoFixture

Question

I am using AutoFixture and I would like to use a specific constructor.

I have the following code, and I like to select a constructor using ITemplateParameterHandler.

public sealed class TemplateSegmentHandler : ITemplateSegmentHandler { public TemplateSegmentHandler(ITemplateIterator iterator) : this(new TemplateParameterHandler(iterator)) { Contract.Requires(iterator != null); } public TemplateSegmentHandler(ITemplateParameterHandler parameterHandler) { Contract.Requires(parameterHandler != null); _parameterHandler = parameterHandler; _parameterHandler.Ending += EndingParameter; } // ... } 

EDIT:

I want to introduce the following fake implementation. (I use NSubstitute to create a fake object.)

 public sealed class CustomTemplateParameter : ICustomization { private readonly ITemplateParameterHandler _context; public CustomTemplateParameter() { _context = Substitute.For<ITemplateParameterHandler>(); } public void Customize(IFixture fixture) { fixture.Customize<ITemplateParameterHandler>(c => c.FromFactory(() => _context)); } public CustomTemplateParameter SetCatchAll(bool isCatchAll) { _context.IsCatchAll.Returns(isCatchAll); return this; } } 

This is how I try to use it.

 [Fact] public void Should_return_true_when_the_segment_has_a_catch_all_parameter() { TemplateSegmentHandler segmentHandler = new Fixture().Customize(new TemplateSegmentHandlerFixture()) .Customize(new CustomTemplateParameterHandler() .SetCatchAll(true)) .Create<TemplateSegmentHandler>(); segmentHandler.Parameter.Start(); segmentHandler.Parameter.End(); segmentHandler.HasCatchAll.Should().BeTrue(); } 

But he still chooses the wrong constructor, and I get the following error.

 Ploeh.AutoFixture.ObjectCreationExceptionAutoFixture was unable to create an instance from Somia.Web.Routing.Template.ITemplateIterator, most likely because it has no public constructor, is an abstract or non-public type. Request path: Somia.Web.Routing.Template.TemplateSegmentHandler --> Somia.Web.Routing.Template.ITemplateIterator iterator --> Somia.Web.Routing.Template.ITemplateIterator 

Answer 1

I finished implementing IMethodQuery and selected the required ctor.

 public sealed class SelectedFirstConstructorQuery : IMethodQuery { private readonly Type _type; public SelectedFirstConstructorQuery(Type type) { _type = type; } public IEnumerable<IMethod> SelectMethods(Type type) { if (type == null) { throw new ArgumentNullException("type"); } return from ci in type.GetConstructors() let parameter = ci.GetParameters().First() where parameter.ParameterType == _type select new ConstructorMethod(ci) as IMethod; } } 

Using:

 fixture.Customize<TemplateSegmentHandler>(c => c.FromFactory(new MethodInvoker(new SelectedFirstConstructorQuery(typeof(ITemplateParameterHandler))))); 

Answer 2

One possible way:

 var parameterHandler = fixture.Create<ITemplateParameterHandler>(); var segmentHandler = fixture.Build<TemplateSegmentHandler>() .FromFactory(() => new TemplateSegmentHandler(parameterHandler)); fixture.Inject(segmentHandler);