Testing custom exception with NUnit

Question

I'm having trouble testing my custom Exception with NUnit. For context, I'm building a simple airport program to improve C#, which I started learning recently. Planes can't land in the airport if it's stormy or if the airport is full. Extracts of the relevant code:

Extract from Airport class with Exceptions:

 public void Land(Plane plane)
        {
            try
            {
                if (weather.Forecast() == "stormy")
                {
                    throw new StormyException("It's too stormy to land");
                }
                if (planes.Count >= _Capacity)
                {
                    throw new CapacityException("Airport is full");
                }
                planes.Add(plane);
                Console.WriteLine($"{ plane.Name } has landed at {_AirportName}");
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
        }

Example of the Exceptions themselves:

   class StormyException : Exception
    {

        public StormyException(string message)
           : base(String.Format(message))
        {

        }

    }

Example of a failing test:

   [Test]

        public void PlaneWontLandIfStormy()
        {
            var weather = new Mock<Weather>();
            weather.Setup(x => x.Forecast()).Returns("stormy");
            var airport = new Airport("TestAirport", weather.Object, 10);
            var exception = Assert.Throws<Exception>(() => airport.Land(plane));
            Assert.AreEqual(exception.Message, "It's too stormy to land");
        }

When I run the program, everything works fine. However this test does not pass, with this error: Expected: <System.Exception> But was: null . I have looked into this and seen syntax along the lines of [ExpectedException] ... but I cannot seem to solve the problem. I'm very new to C# so any help would be much appreciated, thank you!

Answer 1

Your Land method need to throw the exception, not catch it.

public void Land(Plane plane)
{
    if (weather.Forecast() == "stormy")
    {
        throw new StormyException("It's too stormy to land");
    }
    if (planes.Count >= _Capacity)
    {
        throw new CapacityException("Airport is full");
    }
    planes.Add(plane);
    Console.WriteLine($"{ plane.Name } has landed at {_AirportName}");
}

Answer 2

in your test

var exception = Assert.Throws< StormyException >(() => airport.Land(plane)); Assert.AreEqual(exception.Message, "It's too stormy to land");

or

var exception = Assert.Throws< StormyException >(() => airport.Land(plane)); exception.Message.Equals("It's too stormy to land");