Question

I’m trying to set up unit tests for a card game application, but my code is throwing a NullReferenceException: Object reference not set to an instance of an object. As far as I can tell I should not be getting this error, but there it is.

Here is my code:

        [TestFixture]
        public class Tests
        {
            CardTable aTable = null;

            [SetUp]
            public void setup()
            {
                aTable = new CardTable();
            }


            [Test]
            public void setPlayerGold_setTo0_return0()
            {
                //arrange

                //act
                aTable.setPlayerGold(0);


                //assert
                Assert.AreEqual(0, aTable.playerGold);
            }
       }

       public class CardTable
       {
           int playerGold;

           public CardTable()
           {
               playerGold = 0;
           }


            public void setPlayerGold(int amount)
            {
               if (amount == 0)
               {
                    playerGold = 0;
               }
               else
               {
                   playerGold += amount;
               }
               goldLabel.Text = playerGold + "";
            }

The exception gets thrown at the aTable.setup line as though aTable was not instantiated, even though it clearly was in the [Setup], and I can’t figure out why. When I remove the ‘act’ call, the test passes, so aTable cannot be null or the test would fail there as well.

I am running Visual C# 2010 Express v10.0.40219.1 SP1Rel with NUnit 2.6.0.12051.

Any help would be appreciated.
Thanks!

Answer 1

I believe it’s in the goldLabel.Text You aren’t instantiating a form anywhere, so the controls on the form are null.

As a general rule, you probably don’t want to test that a label is set to a value in your unit tests, instead somehow mock this object or just write a test that a value is set (but not that a label’s text is updated.)