Create object hierarchy for test

Question

I building a test-driven application that will sort a flat file into a parent-child-hierarchy. And now I want to create a pretty generic test for my own sorting. For that I want to generate some test data, which I then sort.

The object that will be sorted will look something like this:

public interface IHierarchicalUnitWithChildren
{
    string Id { get; }
    string ParentId { get; }
    IList<IHierarchicalUnitWithChildren> Children { get; set; }
}

But I don't want to create the test-object myself. I want this to be generated by code, as such:

        _items = new List<IHierarchicalUnitWithChildren>();
        Random random = new Random();

        for (int i = 1; i < 1000; i++)
        {
            var item = new HierarchicalUnitMock()
            {
                Oid = i.ToString(),
                Children = new List<IHierarchicalUnit>(),
            };

            // We need a couple of roots.
            if (i%100 != 0)
            {
                item.Poid = random.Next(1, 100).ToString();
            }

            _items.Add(item);
        }

I can easily generate a thousand items, but I also need to give them a valid parent. How can I make sure that I'm creating a valid structure, where I have a couple of roots and all children have parents that are valid.

No item should have a parent that is a child (or grandchild) of itself and thus making it an infinite hierachy.

Or am I thinking about it all wrong? Should a test always have static data?

UPDATE:

Is there any way to do this with a smart loop, that always generate the same data? So that the test-case always will be the same?

Answer 1

Randomly live-generated data in tests is not a good idea. there's no way you can guarantee the test conditions will be the same every time, and no guarantee that you cover every possible scenario.

Instead:

Think about what your code does, break it down into pseudo code if you have to, and try to come up with scenarios that could break it. make your test data set specifically to cause these conditions.