Unit testing with NUnit. Null object error

Question

I keep getting a null object reference error when im running one of my unit test.

Unit Test:

    [Test]
    public void EnumeratedData_ValidInputType_NoErrorAdded()
    {
        List<String> errorMessageList = new List<string>();
        UserInputEntity myEntity = new UserInputEntity();

        myEntity.DataTypes = new List<string>();
        myEntity.DataTypes.Add("DateTime");
        myEntity.DataTypes.Add("datetime");
        myEntity.DataTypes.Add("decimal");
        myEntity.DataTypes.Add("decIMAL");
        myEntity.DataTypes.Add("DOUble");
        myEntity.DataTypes.Add("double");
        myEntity.DataTypes.Add("FLOat");
        myEntity.DataTypes.Add("float");
        myEntity.DataTypes.Add("INT");
        myEntity.DataTypes.Add("int");

        PathReader reader = new PathReader();
        IOManager manager = new IOManager(reader);
        VerificationManager testObject = new VerificationManager(manager);

        testObject.EnumeratedDataTypes(myEntity, errorMessageList);
        Assert.AreEqual(errorMessageList.Count, 0);
    }

Method Code:

    public void EnumeratedDataTypes(UserInputEntity inputs, List<String> errorMessageList)
    {
        inputs.EnumeratedDataTypes = new int[inputs.DataTypes.Count];
        try
        {
            for (int i = 0; i < inputs.DataTypes.Count; i++)
            {
                inputs.EnumeratedDataTypes[i] = (int)Enum.Parse(typeof(Enumerations.ColumnDataTypes), inputs.DataTypes[i].ToUpper());
            }
        }
        catch (Exception ex)
        {
            errorMessageList.Add(ex.Message);
        }
    }

Enum:

class Enumerations
{
    public enum ColumnDataTypes
    {
        DATETIME = 0,
        DECIMAL = 1,
        DOUBLE = 2,
        FLOAT = 3,
        INT = 4
    }
}

ErrorMessage:

FrazerMann.CsvImporter.Entity.Test.EntityVerificationTests.EnumeratedData_ValidInputType_NoErrorAdded: System.NullReferenceException : Object reference not set to an instance of an object.

Im assumin im overlooking something stupidly simple but i cant see it. id appreciate it if someone could put me out of my misery.

Anders Gustafsson · Accepted Answer · 2012-08-08 14:53:05Z

1

In your EnumeratedDataTypes method, you first set the length of the inputs.EnumeratedDataTypes property to inputs.ColumnNames.Count, which is equal to 0 since it has not been filled with data yet (it is only the List capacity that has been set to 9).

Next, when filling this array property with data you loop from 0 to index (including) inputs.DataTypes.Count:

for (int i = 0; i <= inputs.DataTypes.Count; i++)

I count the size of the input.DataTypes list to 10. Thus, you will try to write data to an empty array.

I propose the following changes:

First, initialize the inputs.EnumeratedDataTypes array as follows:

inputs.EnumeratedDataTypes = new int[inputs.DataTypes.Count];

Second, use < instead of <= in the for loop:

for (int i = 0; i < inputs.DataTypes.Count; i++)

edited Aug 8, 2012 at 14:53

answered Aug 8, 2012 at 14:37

Anders Gustafsson

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5 Comments

JTMon Over a year ago

@Andres you beat me to the answer. Just one clarification, the count is actually 0 as the list has not been used yet.

Anders Gustafsson Over a year ago

@JTMon You are right, sorry! It is of course the List capacity that is being set in the constructor, not the predefined size. Will update my response accordingly.

Hans Rudel Over a year ago

Anders, cheers for replying. Good point about the <= and initializing. Unfortunately its still saying i have an error of the same type. Ill edit my original question with he updated code. +1 though :)

Anders Gustafsson Over a year ago

Do you have more information as to exactly where the exception is thrown? It is not obvious that any part of your code should throw NullReferenceException. Could it be that any of the constructors you are calling throws? I am thinking of the reader, manager and testObject initializers.

Hans Rudel Over a year ago

Weird, i just reverted back to a previous version, made those changes u suggested and then re-ran the tests and it works. Thanks so much for your help, i really appreciate it!

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