Question

I have a method similar to this:

public List<MyClass> DoSomething(string Name, string Address, string Email, ref string ErrorMessage)
{
  //Check for empty string parameters etc now go and get some data   
  List<MyClass> Data = GetData(Name, Address, Email);

  /*************************************************************    
  //How do I unit test that the data variable might be empty???    
  *************************************************************/

  List<MyClass> FormattedData = FormatData(Data);
  return FormattedData;
}

I’m just learning TDD/Unit Testing. My question is, how do I write a test to ensure that if GetData returns an empty list I set ErrorMessage to something and then return a empty list?

Answer 1

When developing you should have left an “entrance point” for testing like this:

public List<MyClass> DoSomething(string Name, string Address,
              string Email, ref string ErrorMessage, IDataProvider provider)
{
  //Check for empty string parameters etc now go and get some data   
  List<MyClass> Data = provider.GetData(Name, Address, Email);

  List<MyClass> FormattedData = FormatData(Data);
  return FormattedData;
}

And in the Unit Testing you should mock the IDataProvider

It’s called Dependency Injection (DI) or Inversion Of Control (IOC)

common mocking library:

• NMock
• EasyMock.NET
• TypeMock Isolator Commercial / Paid
• Rhino Mocks
• Moq
• NSubstitute
• JustMock Commercial / Paid
• FakeItEasy
• Moles

The list was taken from here

Wikipedia articles:

Dependency Injection
Inversion Of Control

---

NUnit pseudo code:

[Test]
public void When_user_forgot_password_should_save_user()
{
    // Arrange
    var errorMessage = string.Empty;
    var dataProvider = MockRepository.GenerateStub<IDataProvider>();
    dataProvider.Stub(x => x.GetData("x", "y", "z", ref errorMessage )).Return(null);

    // Act
    var result DoSomething("x","y","z", ref errorMessage, dataProvider);

    // Assert

    //...
}