You are naming your tests wrong

1.cs

[MethodUnderTest]_[Scenario]_[ExpectedResult]

10.cs

public void Delivery_with_a_past_date_is_invalid()

2.cs

public class CalculatorTests
{
    [Fact]
    public void Sum_of_two_numbers()
    {
        double first = 10;
        double second = 20;
        var sut = new Calculator();
        
        double result = sut.Sum(first, second);
        
        Assert.Equal(30, result);
    }
}

3.cs

public void Sum_TwoNumbers_ReturnsSum()

4.cs

public void Sum_of_two_numbers()
public void Sum_TwoNumbers_ReturnsSum()

5.cs

[Fact]
public void IsDeliveryValid_InvalidDate_ReturnsFalse()
{
    DeliveryService sut = new DeliveryService();
    DateTime pastDate = DateTime.Now.AddDays(-1);
    Delivery delivery = new Delivery
    {
        Date = pastDate
    };
    
    bool isValid = sut.IsDeliveryValid(delivery);
    
    Assert.False(isValid);
}

6.cs

public void Delivery_with_invalid_date_should_be_considered_invalid()

7.cs

public void Delivery_with_past_date_should_be_considered_invalid()

8.cs

public void Delivery_with_past_date_should_be_invalid()

9.cs

public void Delivery_with_past_date_is_invalid()