StepDefinition filter attributes

[adamralph]

An extensibility point to allow the filtering of step definitions in a scenario before execution.

E.g. emulation of the undocumented 1.x ContinueOnFailureAfterAttribute:

[Scenario]
[ContinueAfterThen]
public void Something()
{
    "Given something"
        .f(() => ...);

    "When something"
        .f(() => ...);

    "Then something"
        .f(() => ...);

    "And something else"
        .f(() => ...);

    "And something else again"
        .f(() => ...);
}

// your own custom extension
public class ContinueAfterThenAttribute : Attribute, IFilter<IStepDefinition>
{
    public IEnumerable<IStepDefinition> Filter(IEnumerable<IStepDefinition> steps)
    {
        var then = false;
        return steps.Select(step => step.OnFailure(
            then || (then = step.Text.StartsWith("Then ", StringComparison.OrdinalIgnoreCase))
            ? RemainingSteps.Run
            : RemainingSteps.Skip));
    }
}

[adamralph]

@ursenzler any thoughts on the base attribute name?

[ursenzler]

Depends on what else is possible with this attribute.
In this scenario it is not filtering.

Maybe StepConfigurationAttribute? -> method Configure(steps)
Or StepDefinitionAttribute? -> method Define(steps)
Or TweakStepAttribute? -> method Tweak(steps)

[adamralph]

Thanks for the suggestions. 'configuration' may be appropriate. I'm not sure about 'definition' since the steps are already defined, the attribute just adds some extra mutation to them. I think 'tweak' doesn't really convey enough. I also thought about 'customize' but that doesn't really fit. There are no 'standard' steps so every step or list of steps is custom.

I think the reason I initially proposed 'filter' was from the 'pipes and filters' pattern. I.e. in a pipe, a stream is passed into a filter and different stream comes out. I admit that the analogy to physical filters is very loose since a physical filter just removes some constituents from the stream, but it is a recognised term in software, e.g. http://en.wikipedia.org/wiki/Filter_(software) and http://www.eaipatterns.com/PipesAndFilters.html

To fit that pattern properly, the type would look like this:

public abstract class StepDefinitionFilterAttribute : Attribute
{
    public abstract IEnumerable<IStepDefinition> Filter(IEnumerable<IStepDefinition> steps);
}

Moreover, we could also have an int Priority property which allows xbehave to order multiple filters into a pipe.

I guess your custom attribute would look something like:

private class ContinueOnFailureAfterIt : StepDefinitionFilterAttribute
{
    public override IEnumerable<IStepDefinition> Filter(IEnumerable<IStepDefinition> steps)
    {
        var it = false;
        return steps.Select(step =>
        {
            if (it ? it : it = step.Text.StartsWith("It "))
            {
                step.ContinueOnFailure = true;
            }

            return step;
        });
    }
}

It might be possible to improve the API to provide a builder method on IStepDefinition:

private class ContinueOnFailureAfterIt : StepDefinitionFilterAttribute
{
    public override IEnumerable<IStepDefinition> Filter(IEnumerable<IStepDefinition> steps)
    {
        var it = false;
        return steps.Select(step =>
            step.ContinueOnFailure(it ? it : it = step.Text.StartsWith("It ")));
    }
}

I guess some further functional wizardry (using .Aggregate()?) could even remove the local it variable.

[ursenzler]

I like this idea.

[adamralph]

then it shall be done 😃

[adamralph]

@ursenzler I came up with a slightly different way of doing it (I've updated the example in the description).

The step builder method is now OnFailure(RemainingSteps) where the RemainingSteps enum has values Skip (default) and Run.

Your custom attribute does not have to inherit from any base attribute. All it has to do is implement IFilter<IStepDefinition>. xBehave will search the assembly, class and method for attributes which implement this interface and will execute them in that order.

The work is done, but not set in stone, so it would be great to hear your thoughts on this before I push out RC3.

[adamralph]

FWIW, RC3 is out - https://www.nuget.org/packages/Xbehave/2.0.0-rc003-build581

There's still time to change things if required.

[adamralph]

https://www.nuget.org/packages/Xbehave/2.0.0

https://github.com/xbehave/xbehave.net/releases/tag/2.0.0