GOAL: Derived Class Use Customizations for Base Class

[mwasson74]

I have scoured the interwebs and I can't seem to find an example that lets the base class customizations apply to each and every derived class. I see lots of examples on how to omit specific properties but I don't want to do that.

Pseudo Code:

fixture.Customize<BaseEntity>(c => c.With(e => e.IsDeleted, false));
var derived = fixture.Create<DerivedClass>();

Assert.False(derived.IsDeleted);

[aivascu]

@mwasson74 there is no "nice" way of doing it using the postprocess composer (aka .Customize<>()) however you can always create a builder tree that does what you require.

var node = new FilteringSpecimenBuilder(
    new FixedBuilder(false),
    new AndRequestSpecification(
        new PropertySpecification(typeof(bool), nameof(MyBaseClass.IsDeleted)),
        new MemberOwnerSpecification(
            new BaseTypeSpecification(typeof(MyBaseClass)))));

Note that I created two custom request specifications for this tree MemberOwnerSpecification that helps identify the owner of the currently processed member and BaseTypeSpecification which validates the type as a child type of a given type.

public class MemberOwnerSpecification : IRequestSpecification
{
    public MemberOwnerSpecification(IRequestSpecification typeSpecification)
    {
        TypeSpecification = typeSpecification
            ?? throw new ArgumentNullException(nameof(typeSpecification));
    }

    public IRequestSpecification TypeSpecification { get; }

    public bool IsSatisfiedBy(object request)
    {
        bool result = request switch
        {
            ParameterInfo parameter => TypeSpecification.IsSatisfiedBy(parameter.Member.ReflectedType),
            PropertyInfo property => TypeSpecification.IsSatisfiedBy(property.ReflectedType),
            FieldInfo field => TypeSpecification.IsSatisfiedBy(field.ReflectedType),
            _ => false
        };

        return result;
    }
}

public class BaseTypeSpecification : IRequestSpecification
{
    public BaseTypeSpecification(Type baseType)
    {
        BaseType = baseType;
    }

    public Type BaseType { get; }

    public bool IsSatisfiedBy(object request)
        => request is Type type
        && this.BaseType.IsAssignableFrom(type);
}

Now given that you have two types MyBaseClass that declares the IsDeleted property and MyChildClass that inherits MyBaseClass, then your test would look something like this.

[Fact]
public void AllGeneratedItemsAreDeleted()
{
    var node = new FilteringSpecimenBuilder(
        new FixedBuilder(false),
        new AndRequestSpecification(
            new PropertySpecification(typeof(bool), nameof(MyBaseClass.IsDeleted)),
            new MemberOwnerSpecification(
                new BaseTypeSpecification(typeof(MyBaseClass)))));

    var fixture = new Fixture();
    fixture.Customizations.Add(node);

    var items = fixture.CreateMany<MyChildClass>(10);

    var areAllFalse = items.All(x => x.IsDeleted == false);

    Assert.True(areAllFalse);
}

Now with a bit more code you could encapsulate that logic in a customization and reuse it in various scenarios.
Let me know if this helps.

[mwasson74]

@aivascu, this helps so much, thank you! 🙏

[MisinformedDNA]

Where are you setting IsDeleted to true? This new PropertySpecification(typeof(bool), nameof(MyBaseClass.IsDeleted)) just identifies that the property exists, correct?

[MisinformedDNA]

Also, do you need to check for the existence of the property, if the base class is guaranteed to have it?

[aivascu]

Where are you setting IsDeleted to true? This new PropertySpecification(typeof(bool), nameof(MyBaseClass.IsDeleted)) just identifies that the property exists, correct?

In this particular case the property was set to false. Notice the FixedBuilder.

Also you don't need to check if the property exists. If a request will match the specification then it will resolve to the value in the specimen builder. If none will match then this builder is skipped entirely.

Guess you could say that the nameof expression is doing the validation in a way.