Mocking common interfaces

Mocking IEnumerable

Mocking an interface that inherits from IEnumerable to return canned data is quite straightforward. Assuming the following classes:

public class DataClass
{
    public int Id { get; set; }
}

public interface IEnumerableClass : IEnumerable<DataClass>
{
}

The following approach can be taken. First, create a list containing the information that needs to be returned by the mock:

IList<DataClass> list = new List<DataClass>();
for (int i = 0; i < 10; i++)
{
    list.Add(new DataClass { Id = 20 + i });
}

Then create a mock of the IEnumerable class and setup its GetEnumerator method to return the list’s enumerator instead:

var mock = new Mock<IEnumerableClass>();
mock.Setup(x => x.GetEnumerator()).Returns(list.GetEnumerator());

This can be validated as follows:

int expected = 20;
foreach (var i in mock.Object)
{
    Assert.AreEqual(expected++, i.Id);
}