I have a need for customizing creation of a collection, with quite complicated relationships between the objects within it, and I can't figure out how to do it correctly.
For the sake of this issue, let's assume I'm working on a todo app. It has Items and SubItems, and the items have a week number indicating when they should be done:
public class Item {
public string Name { get; set; }
public int Week { get; set; }
public ICollection<SubItem> SubItems { get; set; }
}
public class SubItem {
public string Name { get; set; }
public Item Parent { get; set; }
}
Now, because this is what data usually looks like in the actual application, I want to create a collection of Items that has the following properties:
- There are items that have the same name, but different weeks
- There are items that have the same week but different name
- There are sub-items that have the same name, but different parents
In order to do this, I've created a TodoItemSpecimenBuilder : ISpecimenBuilder which starts its Create method like this:
var type = (request as PropertyInfo)?.PropertyType ?? request as Type;
if (type == null || !typeof(IEnumerable<Item>).IsAssignableFrom(type))
{
return new NoSpecimen();
}
// build up the actual collection
return BuildActualCollection();
However, when I run tests with this specimen builder included in my context, I get lots (maybe 20 or 30) hits on the return statement before I enter even my setup code, and the first time I try to actually CreateMany<Item>(), it blows up with a cast exception because it can't cast OmitSpecimen to Item.
What am I doing wrong here?
Full sample code, compilable after installing NUnit and AutoFixture:
public class TodoList
{
public ICollection<Item> Tasks { get; set; }
}
public class Item
{
public string Name { get; set; }
public Week Week { get; set; }
public ICollection<SubItem> SubItems { get; set; }
public int ItemId { get; set; }
public TodoList TodoList { get; set; }
}
public class SubItem
{
public Item Item { get; set; }
public string Name { get; set; }
public int SortOrder { get; set; }
public string HelpText { get; set; }
}
public class Week
{
public int WeekId { get; set; }
}
public class ItemCollectionSpecimenBuilder : ISpecimenBuilder
{
public object Create(object request, ISpecimenContext context)
{
if (!IsApplicable(request))
{
return new NoSpecimen();
}
var items = new List<Item>(3);
var week1 = context.Create<Week>();
var week2 = context.Create<Week>();
items.Add(CreateItem(context, week1));
items.Add(CreateItem(context, week1));
items.Add(CreateItem(context, week2));
items.GroupBy(t => t.Week).ToList().ForEach(ConfigureNames);
ConfigureSubItems(context, items);
return items;
}
private static bool IsApplicable(object request)
{
bool IsManyItemsType(Type type) => typeof(IEnumerable<Item>).IsAssignableFrom(type);
bool IsItemsType(Type type) => type != null && typeof(Item) == type;
switch (request)
{
case PropertyInfo pInfo:
return IsManyItemsType(pInfo.PropertyType);
case Type type:
return IsManyItemsType(type);
case MultipleRequest multipleRequest:
if (!(multipleRequest.Request is SeededRequest seededRequest))
{
return false;
}
return IsItemsType(seededRequest.Request as Type);
default:
return false;
}
}
private static Item CreateItem(ISpecimenContext context, Week week)
{
var item = context.Create<Item>();
item.Week = week;
return item;
}
private static void ConfigureNames(IEnumerable<Item> items)
{
string name = null;
foreach (var item in items)
{
if (name == null)
{
name = item.Name;
}
else
{
item.Name = name;
}
}
}
private static void ConfigureSubItems(ISpecimenContext context, IEnumerable<Item> items)
{
foreach (var group in items.GroupBy(item => item.Week.WeekId))
{
var subItemTemplates = context.CreateMany<SubItem>().ToList();
foreach (var item in group)
{
item.SubItems.Clear();
foreach (var subItem in context.CreateMany<SubItem>().Zip(subItemTemplates,
(model, subItem) =>
{
subItem.Item = item;
subItem.Name = model.Name;
subItem.SortOrder = model.SortOrder;
subItem.HelpText = model.HelpText;
return subItem;
}))
{
item.SubItems.Add(subItem);
}
}
}
}
}
[TestFixture]
public class AutoFixtureSpecimenBuilderTests
{
private static void TestCreationOfTasks(Func<IFixture, ICollection<Item>> creator)
{
var fixture = new Fixture();
fixture.Customizations.Add(new ItemCollectionSpecimenBuilder());
fixture.Behaviors.OfType<ThrowingRecursionBehavior>().ToList()
.ForEach(b => fixture.Behaviors.Remove(b));
fixture.Behaviors.Add(new OmitOnRecursionBehavior());
var tasks = creator(fixture);
Assert.AreEqual(3, tasks.Count);
Assert.AreEqual(2, tasks.GroupBy(t => t.Week).Count());
Assert.IsTrue(tasks.GroupBy(t => t.Week).Select(g => g.Select(t => t.Name).Distinct()).All(distinctNames => distinctNames.Count() == 1));
var task = tasks.GroupBy(t => t.Week).OrderBy(g => g.Count()).First().OrderBy(t => t.ItemId).First();
}
[Test]
public void CreateMany() => TestCreationOfTasks(fixture => fixture.CreateMany<Item>().ToList());
[Test]
public void CreateWithProperty() => TestCreationOfTasks(fixture => fixture.Create<TodoList>().Tasks);
[Test]
public void CreateAsList() => TestCreationOfTasks(fixture => fixture.Create<IList<Item>>());
}
