I want to mock a Linq expression that returns a Dictionary<string, string>

Dictionary<string, string> properties = new Dictionary<string, string>()
{
    { "Service", "serviceTest" }
}

equipment.SetProperties(dmsElement.Properties.ToDictionary(x => x.Definition.Name, x => x.Value));

Here is the unit test

fakeEquipment.Setup(e => e.Properties.ToDictionary(It.IsAny<Func<IDmsElementProperty, string>>(), It.IsAny<Func<IDmsElementProperty, string>>())).Returns(properties);

I am getting the following error:

System.NotSupportedException: 'Unsupported expression: ... => ....ToDictionary<IDmsElementProperty, string, string>(It.IsAny<Func<IDmsElementProperty, string>>(), It.IsAny<Func<IDmsElementProperty, string>>())

How can I setup the ToDictionary method to retrieve the expected values?

CodePudding user response：

You cannot mock the ToDictionary method because it is an extension method found in the System.Enumerable type. That method is going to enumerate your .Properties property no matter what. You can and should, however, mock directly e.Properties.
You can return an implementation of the IPropertyCollection interface, or if it's not that much of a problem write a very simple adapter exposing an underlying collection (be it a dictionary or a list). If you have access to an existing class (say, ListPropertyCollection<T>), you could just instantiate it.