Question

I’m new to unit test and confusing how write unit test method like this:

public Boolean BeepInTime(Interfaces.IDateTime time,TimeSpan beepTime)
{
    Interfaces.IBeep beep= new Beep();
    var h = time.GetTime();
    if (h == beepTime)
    {
       return beep.Beeping();
    }
    else
    {
       return false;
    }
}

public Boolean Beeping()
{
    try
    {
      SystemSounds.Beep.Play();
      return true;
    }
    catch
    {
      return false;
    }
}

When testing BeepInTime , I’d like (beep.Beeping()) not running. I read about stub and think in this case I should use stub but it is confusing about how to do this.
Could you send some source with simple example about stub.

Answer 1

The solution is – dependency injection.

Each time you do or see ... = new ...(); (construction) think of dependency injection, basically explicit instantiation introduces dependencies and then sometimes writing unit tests for such a code becomes not trivial.

So instead of explicit instantiation of Beep class just inject it. What is good – you already have an interface which abstracts this class – IBeep, this would allow you creatign and injecting a mock instead of a real class instance when writing unit tests.

public Boolean BeepInTime(Interfaces.IBeep beeper, TimeSpan beepTime) 
{
    var h = time.GetTime();            
    if (h == beepTime)            
    {                 
        return beep.Beeping();            
    } 

    return false;
}

Ans just imagine how this technique is helpful in case of injecting DB access service or web-service, you do not need a real DB or web-service while writing unit tests – you just mock DB/web service and that’s it.

Example using RhinoMocks:

var mock = MockRepository.GenerateMock<IBeep>();

// setup Beeping() return value == true
mock.Expect(m => m.Beeping()).Return(true);
var isBeepInTime = BeepInTime(mock, timeSpan)