Overriding methods in classes-dependencies

1.cs

public class StatisticsCalculator
{
    public async Task<(double weightDelivered, double totalCost)> Calculate(int customerId)
    {
        List<DeliveryRecord> records = await GetDeliveries(customerId);

        double weightDelivered = records.Sum(x => x.Weight);
        double totalCost = records.Sum(x => x.Cost);

        return (weightDelivered, totalCost);
    }

    public async Task<List<DeliveryRecord>> GetDeliveries(int id)
    {
        var client = new HttpClient();
        string json = await client.GetStringAsync("http://external.provider.com/api/deliveries?customerId=" + id);
        var result = JsonConvert.DeserializeObject<List<DeliveryRecord>>(json);
        return result;
    }
}

2.cs

public class CustomerController
{
    private readonly StatisticsCalculator _calculator;

    public CustomerController(StatisticsCalculator calculator)
    {
        _calculator = calculator;
    }

    public async Task<string> GetStatistics(int customerId)
    {
        (double weightDelivered, double totalCost) = await _calculator.Calculate(customerId);

        return $"Total weight delivered: {weightDelivered}. Total cost: {totalCost}";
    }
}

3.cs

[Fact]
public async Task No_delivery_records_form_correct_result()
{
    // Arrange
    var mock = new Mock<StatisticsCalculator> { CallBase = true };
    mock.Setup(x => x.GetDeliveries(It.IsAny<int>()))
        .Returns(Task.FromResult(new List<DeliveryRecord>()));
    var controller = new CustomerController(mock.Object);

    // Act
    string result = await controller.GetStatistics(1);

    // Assert
    Assert.Equal("Total weight delivered: 0. Total cost: 0", result);
}

4.cs

new Mock<StatisticsCalculator> { CallBase = true }; // Preserves the base class behavior

5.cs

public class DeliveryGateway : IDeliveryGateway
{
    public async Task<List<DeliveryRecord>> GetDeliveries(int customerId)
    {
        var client = new HttpClient();
        string json = await client.GetStringAsync("http://external.provider.com/api/deliveries?customerId=" + customerId);
        var result = JsonConvert.DeserializeObject<List<DeliveryRecord>>(json);
        return result;
    }
}

public class StatisticsCalculator
{
    public (double weightDelivered, double totalCost) Calculate(List<DeliveryRecord> records)
    {
        double weightDelivered = records.Sum(x => x.Weight);
        double totalCost = records.Sum(x => x.Cost);

        return (weightDelivered, totalCost);
    }
}

6.cs

public class CustomerController
{
    private readonly StatisticsCalculator _calculator;
    private readonly IDeliveryGateway _gateway;

    public CustomerController(StatisticsCalculator calculator, IDeliveryGateway gateway)
    {
        _calculator = calculator;
        _gateway = gateway;
    }

    public async Task<string> GetStatistics(int customerId)
    {
        List<DeliveryRecord> records = await _gateway.GetDeliveries(customerId);
        (double weightDelivered, double totalCost) = _calculator.Calculate(records);

        return $"Total weight delivered: {weightDelivered}. Total cost: {totalCost}";
    }
}