AutoFixture CompositeDataAttribute does not work with PropertyDataAttribute

Question

I'm trying to create AutoPropertyDataAttribute based on CompositeDataAttribute from this example AutoFixture: PropertyData and heterogeneous parameters.

It works with single set of parameters, but fails with more sets of parameters. Here is code:

public static IEnumerable<object[]> NumericSequence
{
    get
    {
        yield return new object[] {1};
        //yield return new object[] {2};
    }
}

[Theory]
[AutoPropertyData("NumericSequence")]
public void Test(int? p1, int? p2, int? p3)
{
    Assert.NotNull(p1);
    Assert.NotNull(p2);
}

public class AutoPropertyDataAttribute : CompositeDataAttribute
{
    public AutoPropertyDataAttribute(string propertyName)
        : base(
              new DataAttribute[] { 
                  new PropertyDataAttribute(propertyName), 
                  new AutoDataAttribute()
              })
    {
    }
}

Trying to uncomment the second yield will break test with message:

System.InvalidOperationException: Expected 2 parameters, got 1 parameters
   at Ploeh.AutoFixture.Xunit.CompositeDataAttribute.<GetData>d__0.MoveNext()
   at Xunit.Extensions.TheoryAttribute.<GetData>d__7.MoveNext()
   at Xunit.Extensions.TheoryAttribute.EnumerateTestCommands(IMethodInfo method)

Same happens with ClassDataAttribute

Answer 1

What actually happens

The NumericSequence [PropertyData] defines two iterations.

The composition of NumericSequence [PropertyData] with [AutoData] assumes that there is enough data on each iteration.

However, the actual composition is:

1st iteration:  [PropertyData], [AutoData]

2nd iteration:  [PropertyData], [n/a]

That's why in the 2nd iteration you eventually run out of data.

Composition

The CompositeDataAttribute respects the LSP in a sense that it is programmed against the base of all data theories, the DataAttribute class.

(That is, there is no assumption that all attributes are composed with [AutoData] at the end.)

For that reason, it can't simply jump from the 2nd iteration to the 1st iteration and grab some [AutoData] values – that would break the LSP.

What you could do

Make the actual composition look like:

1st iteration:  [PropertyData], [AutoData]

2nd iteration:  [PropertyData], [AutoData]

By defining two properties:

public static IEnumerable<object[]> FirstPropertyData { get { 
    yield return new object[] { 1 }; } }

public static IEnumerable<object[]> OtherPropertyData { get { 
    yield return new object[] { 9 }; } }

And then, the original test can be written as:

[Theory]
[AutoPropertyData("FirstPropertyData")]
[AutoPropertyData("OtherPropertyData")]
public void Test(int n1, int n2, int n3)
{
}

The test executes twice and n1 is always supplied by [PropertyData] while n2 and n3 are always supplied by [AutoData].

Answer 2

I ran into this issue and decided to implement a custom DataAttribute to solve the problem. I couldn't use either attribute as a base class (reasons below) so I just took the things I needed from the source of each. Thank you OSS :)

Things to note:

• I wanted to change the semantics slightly so that I had the option of yielding single objects rather than arrays. Just makes code look neater for single-object parameters. This meant I couldn't use PropertyDataAttribute as a base class
• The fixture needs to be created every time a new set of parameters is generated. This meant I couldn't use AutoDataAttribute as a base class

Gist

Or inline source below:

public class AutoPropertyDataAttribute : DataAttribute
{
    private readonly string _propertyName;
    private readonly Func<IFixture> _createFixture;

    public AutoPropertyDataAttribute(string propertyName)
        : this(propertyName, () => new Fixture())
    { }

    protected AutoPropertyDataAttribute(string propertyName, Func<IFixture> createFixture)
    {
        _propertyName = propertyName;
        _createFixture = createFixture;
    }

    public Type PropertyHost { get; set; }

    private IEnumerable<object[]> GetAllParameterObjects(MethodInfo methodUnderTest)
    {
        var type = PropertyHost ?? methodUnderTest.DeclaringType;
        var property = type.GetProperty(_propertyName, BindingFlags.Static | BindingFlags.Public | BindingFlags.FlattenHierarchy);

        if (property == null)
            throw new ArgumentException(string.Format("Could not find public static property {0} on {1}", _propertyName, type.FullName));
        var obj = property.GetValue(null, null);
        if (obj == null)
            return null;

        var enumerable = obj as IEnumerable<object[]>;
        if (enumerable != null)
            return enumerable;

        var singleEnumerable = obj as IEnumerable<object>;
        if (singleEnumerable != null)
            return singleEnumerable.Select(x => new[] {x});

        throw new ArgumentException(string.Format("Property {0} on {1} did not return IEnumerable<object[]>", _propertyName, type.FullName));
    }

    private object[] GetObjects(object[] parameterized, ParameterInfo[] parameters, IFixture fixture)
    {
        var result = new object[parameters.Length];

        for (int i = 0; i < parameters.Length; i++)
        {
            if (i < parameterized.Length)
                result[i] = parameterized[i];
            else
                result[i] = CustomizeAndCreate(fixture, parameters[i]);
        }

        return result;
    }

    private object CustomizeAndCreate(IFixture fixture, ParameterInfo p)
    {
        var customizations = p.GetCustomAttributes(typeof (CustomizeAttribute), false)
            .OfType<CustomizeAttribute>()
            .Select(attr => attr.GetCustomization(p));

        foreach (var c in customizations)
        {
            fixture.Customize(c);
        }

        var context = new SpecimenContext(fixture);
        return context.Resolve(p);
    }

    public override IEnumerable<object[]> GetData(MethodInfo methodUnderTest, Type[] parameterTypes)
    {
        foreach (var values in GetAllParameterObjects(methodUnderTest))
        {
            yield return GetObjects(values, methodUnderTest.GetParameters(), _createFixture());
        }
    }
}

Answer 3

As a workaround you can restructure the AutoPropertyDataAttribute a bit and use the CompositeDataAttribute internally, rather than deriving from it. Derive from the PropertyDataAttribute instead:

public class AutoPropertyDataAttribute : PropertyDataAttribute
{
    public AutoPropertyDataAttribute(string propertyName)
            : base(propertyName)
    {
    }

Then override the GetData method to loop over the values returned by the PropertyDataAttribute, and leverage AutoFixture's InlineAutoData(which derives from CompositeDataAttribute) to fill in the rest of the parameters:

    public override IEnumerable<object[]> GetData(System.Reflection.MethodInfo methodUnderTest, Type[] parameterTypes)
    {
        foreach (var values in base.GetData(methodUnderTest, parameterTypes))
        {
            // The params returned by the base class are the first m params, 
            // and the rest of the params can be satisfied by AutoFixture using
            // its InlineAutoDataAttribute class.
            var iada = new InlineAutoDataAttribute(values);
            foreach (var parameters in iada.GetData(methodUnderTest, parameterTypes))
                yield return parameters;
        }
    }

The outer loop iterates over the values returned by the PropertyData (each iteration is a row, with some of the cells filled in). The inner loop fills in the remaining cells.

It's not the prettiest thing, but it seems to work. I like Mark's idea to have AutoFixture try to fill in the remaining cells. One less piece of glue code to write :)

Hope this helps,
Jeff.