How to write a conceptually correct unit test for API method with Linq?

I'm learning how to write unit tests, please don't judge heavily. I have an API method below, written in C# for .NET 8.0, which I want to test. I use XUnit, Entity Framework Core 8, SQL Server 2019. Currently I'm rewriting it to separate the data layer, so I will not have to moq DB context.

[HttpGet("GetABunch")]
public async Task<ActionResult<TodoItem>> GetABunch()
{
    string[] myAnimals = { "dog", "cat" };

    var animals = await _context.TodoItems
        .Where(i => myAnimals.Contains(i.Name))
        .ToListAsync();

    return Ok(animals);
}

My unit test is not working. I'm getting an error:

System.ArgumentException : Can not instantiate proxy of class: TodoApiDb.Models.TodoContext.
Could not find a parameterless constructor. (Parameter 'constructorArguments')

But before fighting this error, and creating context constructor without parameters, I believe my test is conceptually wrong, please help to fix it.

Here's my unit test:

[Fact]
public async Task GetABunch_ReturnsFilteredTodoItems()
{
    // Arrange
    var mockData = new List<TodoItem>
    {
        new TodoItem { Id = 1, Name = "dog" },
        new TodoItem { Id = 2, Name = "cat" },
        new TodoItem { Id = 3, Name = "bird" }
    }.AsQueryable();

    var mockSet = new Mock<DbSet<TodoItem>>();
    mockSet.As<IQueryable<TodoItem>>().Setup(m => m.Provider).Returns(mockData.Provider);
    mockSet.As<IQueryable<TodoItem>>().Setup(m => m.Expression).Returns(mockData.Expression);
    mockSet.As<IQueryable<TodoItem>>().Setup(m => m.ElementType).Returns(mockData.ElementType);
    mockSet.As<IQueryable<TodoItem>>().Setup(m => m.GetEnumerator()).Returns(mockData.GetEnumerator());
    mockSet.As<IAsyncEnumerable<TodoItem>>().Setup(m => m.GetAsyncEnumerator(It.IsAny<CancellationToken>()))
        .Returns(new TestAsyncEnumerator<TodoItem>(mockData.GetEnumerator()));

    var mockContext = new Mock<TodoContext>();
    //mockContext.Setup(c => c.TodoItems).Returns(mockSet.Object);
    mockContext.Setup(c => c.Set<TodoItem>()).Returns(mockSet.Object);

    var controller = new TodoItemsController(mockContext.Object);

    // Act
    var result = await controller.GetABunch();

    // Assert
    var actionResult = Assert.IsType<OkObjectResult>(result.Result);
    var returnedItems = Assert.IsType<List<TodoItem>>(actionResult.Value);
    Assert.Equal(2, returnedItems.Count);
    Assert.Contains(returnedItems, i => i.Name == "dog");
    Assert.Contains(returnedItems, i => i.Name == "cat");
}

Testing app code on GitHub.