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When unit testing you should try to test the class of interest in isolation, this means removing any dependencies with other components; for example I needed to test in isolation a class that is instanciated by passing to it an object that implements IDataReader.

public DictionaryItem(IDataReader)

By creating a mock object for IDataReader, the class can be tested in isolation of the Data Access Layer (DAL).

You could either create the necessary mock object, by building your own class implementing IDataReader or use a mock object framework to help you.
For some time now NMock has been regarded as a powerful framework for generating mock objects, however the original NMock had a few limitations, one of which seemed to prevent nmock from being used to test a class that exposed an indexer. Fortunately NMock2 the new version of nmock, solves this problem. NMock2 is a total re-write micking jMock were “expectations are expressed in a more conversational style”; this makes NMock to easier to work with than its predecessor.

The following code creates the dataReaderMock mock object, which can then be passed to my DictionaryItem class in my unit test;

Mockery mocks = new Mockery();

IDataReader dataReaderMock = (IDataReader)mocks.NewMock(typeof(IDataReader));

Expect.AtLeastOnce.On(dataReaderMock).Method(”Read”).Will(Return.Value(true));
Expect.Once.On(dataReaderMock).Method(”Read”).Will(Return.Value(false));
Expect.Once.On(dataReaderMock).Method(”NextResult”).Will(Return.Value(false));
Expect.Once.On(dataReaderMock).GetProperty(”IsClosed”).Will(Return.Value(false));
Expect.Once.On(dataReaderMock).Method(”Close”);

Expect.Once.On(dataReaderMock).Get[”COL_1″].Will(Return.Value(4));
Expect.Once.On(dataReaderMock).Get[”COL_2″].Will(Return.Value(”col1ValueExpectedByUnitTest”));
Expect.Once.On(dataReaderMock).Get[”COL_3″].Will(Return.Value(”col2ValueExpectedByUnitTest”));
return dataReaderMock;

As you can see the expectations on a Mock2 object are easy to read; at least one expectation is made for each propety or method you expect to be called. The expectations reflect how the constructor of DictionaryItem will use the IDataReader; in my case the mock object reflects an DataReader with only one DataRow. The first part of the expectation defines how many times you expect the method to be called “Expect.AtLeastOnce.On”, the second part defines the name of the method, property or indexer expected to be called “Method(”Read”)” and the last part defines what value should be returned “Will(Return.Value(true))”.
If you use the mock object an nunit test if any of the expectations have not been met, the test will fail.

Download NMock2, NMock2 Tutorial