Testing if a collection contains objects based on a particular property

Question

I'm using NUnit 2.5.7. I want to test whether a collection of custom objects of a particular class contains certain objects, based on one of the class's properties.

e.g. a contrived example...

public class Person
{
    public string Name { get; set; }

    public Person(string name)
    {
        Name = name;
    }
}

// ...

public List<Person> GetFavouritePeople()
{
   List<Person> favouritePeople = new List<Person>();
   favouritePeople.Add(new Person("joe"));
   favouritePeople.Add(new Person("fred"));
   favouritePeople.Add(new Person("jenny"));

   return favouritePeople;
}

// ... 

[Test]
public GetFavouritePeople()
{
    List<Person> people = GetFavouritePeople();

    // What I'd like to test, but not sure how to do it...
    Assert.Contains(Name="joe", people);
    Assert.Contains(Name="fred", people);
    Assert.Contains(Name="jenny", people);
}

Although it would be simple enough in this example, I don't want to create mock objects for each Person and use those in the assertion... I just want to check based on a particular property (Name in this example.)

Answer 1

You could use LINQ:

Assert.That(people.Any(p => p.Name == "joe"));

or, if you want to be explicit about there being exactly one person with each name:

Assert.That(people.Count(p => p.Name == "joe"), Is.EqualTo(1));

If you want a better error message than "Assertion failed, expected true, was false", you could create your own assert method.

For several collection-related asserts, CollectionAssert is very useful - for instance, it allows you to check if two collections contain the same elements, irrespective of their order. So yet another possibility is:

CollectionAssert.AreEquivalent(new[] {"joe", "fred", "jenny"}, people.Select(p => p.Name).ToList());

Note that CollectionAssert.AreEquivalent() is a little picky with regard to the types it accepts (even though the signature takes IEnumerable). I usually wrap it in another method that calls ToList() on both parameters before invoking CollectionAssert.AreEquivalent().