Writing Custom Data Source Attributes in MbUnit v3.2

The extensibility of the Gallio platform is simply amazing. You can virtually extend any part of the system. It goes from a simple plugin that provides new handy functionalities to a full-blown adapter for your fancy testing framework. Today, I would like to explain how easy it is to extend the MbUnit framework with a custom data source attribute.

MbUnit has many useful built-in data source attributes which might be used to create powerful data-driven tests. The most popular attributes are certainly [Row] and [Column].

Now let's imagine you get bored with writing that kind of tests:

[Test]
public void Mytest(
  [Column(true, false)] bool flag1, 
  [Column(true, false)] bool flag2, 
  [Column(true, false)] bool flag3)
{
  // ...
}

Imagine how beautiful would be the world if you could write the following instead:

[Test]
public void Mytest(
  [BooleanData] bool flag1, 
  [BooleanData] bool flag2, 
  [BooleanData] bool flag3)
{
  // ...
}

Unfortunately, this data source attribute does not exist in MbUnit.

So let's make it happen!

Creating a custom data source is very easy. Basically you simply need to derive from MbUnit.Framework.DataAttribute, and to override the virtual method PopulateDataSource.

[AttributeUsage(PatternAttributeTargets.DataContext, AllowMultiple = false, Inherited = true)]
public class BooleanDataAttribute : DataAttribute
{
  protected override void PopulateDataSource(IPatternScope scope, DataSource dataSource, ICodeElementInfo codeElement)
  {
    dataSource.AddDataSet(new ValueSequenceDataSet(new object[] { true, false }, GetMetadata(), false));
  }
}

That's all. Compile and run your test happily!

You might find more inspiration by examining the actual implementation of existing built-in attributes such as [EnumData] or [RandomStrings] which is slightly more complicated as it relies on the underlying Gallio data generation framework.

Next time, I will explain how to properly test you custom data source attribute by using the Gallio SDK.