Automapper cannot map asynchronously

Question

I have an async method:

public async Task<TProjection> GetById<TProjection>(int id)
{
    return await Collection
        .Where(entity => entity.Id == id)
        .ProjectTo<TProjection>()
        .ToListAsync();
}

That I need to unit test, which I am doing thanks to the answer here

However, attempting to project to a TestEntity causes the following exception to be thrown:

Unable to cast object of type 'TestDbAsyncEnumerable'1[Models.Entity]' to type 'System.Linq.IQueryable'1[TestSpecNamespace+TestEntity]'.

Here is the test:

[Theory]//And then a bunch of ids
public async Task GetSubEntities_Projects_IdExists(int id)
{
    Mapper.Initialize(cfg => { cfg.CreateMap<Entity, TestEntity>(); });
    var mockContext = CreateMockContext();
    var provider = TestProvider.Create(context: mockContext.Object);

    var response = await provider.GetById<TestEntity>(id); //Calls the aforementioned

    //Asserts
}