Why does adding a constructor fail this MSpec test with System.InvalidOperationException?

Question

I have this first version of a class

public class GenerateAuthorisationWorkflows : IGenerateAuthorisationWorkflows
{
    public IList<Guid> FromDtaObjects(IList<DtaObject> dtaObjects, Employee requestingEmployee)
    {
        foreach (var dtaObject in dtaObjects) { }
        return new List<Guid>();
    }

    public IList<Guid> FromDtaObjects()
    {
        return new List<Guid>();
    }
}

And the MSpec tests for it

public abstract class specification_for_generate_workflows : Specification<GenerateAuthorisationWorkflows>
{
    protected static IWorkflowService workflowService;

    Establish context = () => { workflowService = DependencyOf<IWorkflowService>(); };
}

[Subject(typeof(GenerateAuthorisationWorkflows))]
public class when_generate_workflows_is_called_with_a_dta_object_list_and_an_employee : specification_for_generate_workflows
{
    static IList<Guid> result;
    static IList<DtaObject> dtaObjects;
    static Employee requestingEmployee;

    Establish context = () =>
    {
         var mocks = new MockRepository();
         var stubDtaObject1 = mocks.Stub<DtaObject>();
         var stubDtaObject2 = mocks.Stub<DtaObject>();
         var dtaObjectEnum = new List<DtaObject>{stubDtaObject1,stubDtaObject2}.GetEnumerator();
         dtaObjects = mocks.Stub<IList<DtaObject>>();
         dtaObjects.Stub(x => x.GetEnumerator()).Return(dtaObjectEnum).WhenCalled(x => x.ReturnValue = dtaObjectEnum);
         requestingEmployee = mocks.Stub<Employee>();
         mocks.ReplayAll();
    };

    Because of = () => result = subject.FromDtaObjects(dtaObjects, requestingEmployee);

    It should_enumerate_the_dta_objects = () => dtaObjects.received(x=> x.GetEnumerator());
    It should_call_workflow_host_helper = () => workflowService.AssertWasCalled(x => x.StartWorkflow());
}

With this configuration, my first test passes and my second test fails, as expected. I added a constructor to the class to inject the IWorkflowService.

public class GenerateAuthorisationWorkflows : IGenerateAuthorisationWorkflows
{
    IWorkflowService _workflowService;

    GenerateAuthorisationWorkflows(IWorkflowService workflowService)
    {
        _workflowService = workflowService;
    }

    public IList<Guid> FromDtaObjects(IList<DtaObject> dtaObjects, Employee requestingEmployee)
    {
        foreach (var dtaObject in dtaObjects)
        {
            Guid workflowKey = _workflowService.StartWorkflow();
        }

        return new List<Guid>();
    }

    public IList<Guid> FromDtaObjects()
    {
        return new List<Guid>();
    }
}

Now, when I run the tests, they fail at the Because:

System.InvalidOperationException: Sequence contains no elements
at System.Linq.Enumerable.First(IEnumerable`1 source)
at MSpecTests.EmployeeRequestSystem.Tasks.Workflows.when_generate_workflows_is_called_with_a_dta_object_list_and_an_employee.<.ctor>b__4() in GenerateAuthorisationWorkflowsSpecs.cs: line 76 

For clarity, line 76 above is:

Because of = () => result = subject.FromDtaObjects(dtaObjects, requestingEmployee);

I've tried tracing the problem but am having no luck. I have tried setting up a constructor that takes no arguments but it raises the same error. I have similar classes with IoC dependencies that work fine using MSpec/Rhino Mocks, where am I going wrong?

Answer 1

Castle Windsor requires a public constructor to instantiate a class. Adding public to the constructor allows correct operation.

public class GenerateAuthorisationWorkflows : IGenerateAuthorisationWorkflows
{
    IWorkflowService _workflowService;

    public GenerateAuthorisationWorkflows(IWorkflowService workflowService)
    {
        _workflowService = workflowService;
    }

    public IList<Guid> FromDtaObjects(IList<DtaObject> dtaObjects, Employee requestingEmployee)
    {
        foreach (var dtaObject in dtaObjects)
        {
            Guid workflowKey = _workflowService.StartWorkflow();
        }

        return new List<Guid>();
    }

    public IList<Guid> FromDtaObjects()
    {
        return new List<Guid>();
    }
}

Answer 2

Rowan, looks like you answered your own question. It's good practice to explicitly state the access modifiers! By default, C# chooses private. These kinds of errors are easy to miss!

I can also see that your Establish block is too complicated. You're testing the implementation details and not the behavior. For example, you are

• stubbing the GetEnumerator call that's implicitly made inside the foreach loop.
• asserting that the workflow service was called only once
• mixing MSpec automocking and your own local mocks

You're not actually testing that you got a GUID for every object in the input list. If I were you, I'd test the behavior like this...

public class GenerateAuthorisationWorkflows : IGenerateAuthorisationWorkflows
{
    private readonly IWorkflowService _service;

    public GenerateAuthorisationWorkflows(IWorkflowService service)
    {
        _service = service;
    }

    public List<Guid> FromDtaObjects(List<DtaObject> input, Employee requestor)
    {
        // I assume that the workflow service generates a new key
        // per input object. So, let's pretend the call looks like
        // this. Also using some LINQ to avoid the foreach or 
        // building up a local list.
        input.Select(x => _service.StartWorkflow(requestor, x)).ToList();
    }
}

[Subject(typeof(GenerateAuthorisationWorkflows))]
public class When_generating_authorisation_keys_for_this_input 
    : Specification<GenerateAuthorisationWorkflows>
{
    private static IWorkflowService _service;
    private static Employee _requestor = new Employee();
    private static List<DtaObject> _input = new List<DtaObject>() 
    {
        new DtaObject(),
        new DtaObject(),
    };
    private static List<Guid> _expected = new List<Guid>()
    {
        Guid.NewGuid(),
        Guid.NewGuid(),
    };

    private static List<Guid> _actual = new List<Guid>();

    Establish context = () =>
    {
        // LINQ that takes each item from each list in a pair. So
        // the service is stubbed to return a specific GUID per 
        // input DtaObject.
        _input.Zip(_expected, (input, output) => 
        {
            DependencyOf<IWorkflowService>().Stub(x => x.StartWorkflow(_requestor, input)).Return(output);
        });
    };

    Because of = () => _actual = Subject.FromDtaObjects(_input, _requestor);

    // This should be an MSpec collection assertion that 
    // ensures that the contents of the collections are
    // equivalent
    It should_get_a_unique_key_per_input = _actual.ShouldEqual(_expected);
}