C# Inline initialization of an IGrouping [duplicate]

Question

If I want to initialize a list of groupings, can I do this inline?

Update with context

I already know I cannot initialize an interface, but is there already an implementation built into dotnet?

I don't want to create my own implementation, because I am trying to refactor an existing private method into its own class which is public, thus I need to pass parameters in for unit testing.

void MyMethod(IList<IGrouping<int, MyObject>> objGroupings)

Currently I have resorted to initializing a list, then grouping by a key:

var fooList = new List<MyObject>
{
     new MyObject{ foo = 5 },
     new MyObject{ foo = 5 },
     new MyObject{ foo = 5 },
     new MyObject{ foo = 2 },
     new MyObject{ foo = 2 }
};

var fooGrouping = fooList.GroupBy(o => o.foo).ToList();

Answer 1

IGrouping is just an interface and cannot be initialised. If you want to use the inline initialisation, you need you initialise an object that implements IGrouping