Strategy pattern with Factory class Unit testing

Question

I was looking for some sample code for unit testing the strategy pattern method invocation.

I have a strategy pattern class LeaveCalculator and based on the leave type the factory class will instantiate the specific calculator.
For the Unit Test part I am trying to verify the proper Leave type calculation is invoked when we call the LeaveCalculator calculate method.

I am using C# for mocking RhinoMocks.

Please let me know any code samples to do this?

public static class LeaveCategoryFactory
{
private static List<ILeaveCalculation> categories = new List<ILeaveCalculation>();

public static ILeaveCalculation GetCategory(LeaveCalculationType calculationType)
{
  if (categories.Count == 0)
  {
    categories = Assembly.GetExecutingAssembly()
                       .GetTypes()
                       .Where(type => typeof(ILeaveCalculation).IsAssignableFrom(type) && type.IsClass)
                       .Select(type => Activator.CreateInstance(type))
                       .Cast<ILeaveCalculation>()
                       .ToList();
  }

  return categories.Where(x => x.CalculationType == calculationType).FirstOrDefault() as ILeaveCalculation;
}
}


[TestMethod]
public void ShouldReturnOneWhenAvailableLeaveCountIs12AndWorkedForAMonth()
{
  leaveCount.StartDate = systemDateTime.Now.Date.AddMonths(-1);
  leaveCount.EndDate = systemDateTime.Now.Date.AddMonths(11);
  leaveCount.Count = 12;
  var proRataClass = MockRepository.GenerateMock<ProRata>();
  var availableLeaveCount = proRataClass.Calculate(employee, systemDateTime.Now.Date, leaveCount);
  Assert.AreEqual(1, availableLeaveCount);
}

It's probably just easier to post the relevant code and tests that show what you're trying to do. It'll be easier for people to help. — Chris Mantle, Aug 19 '13 at 08:53
I don't see how these `LeaveCategoryFactory` and your test method relate to each other at all. I assume `ProRata` is a class? Perhaps it implements `ILeaveCalculation`? One thing does instantly leap out, though: `LeaveCategoryFactory` is static. It's incredibly difficult to test *anything* when you have static classes around. — Chris Mantle, Aug 19 '13 at 19:16
I would like to know what it the best option to create instance of Strategy pattern classes. if I use the static initiator how can I make sure the relevant classes are initiated? — Saanch, Aug 20 '13 at 01:53

Petr Behenský · Accepted Answer · 2013-08-23T11:16:31.560

You have to redesign your code to use Dependency Injection. In your case define ILeaveFactoryCategory with GetCategory method. Make your ProRate class dependent on it (for example set factory by constructor parameter). Then mock the factory interface not calculator itself and set expectations for them. Use mocked object as parameter for class under test (LeaveCalculator). Verify expectations for you mocked object.

ILeaveCalculation expectedCalculator = new MyCalculator();
LeaveCalculationType expectedCalculationType = LeaveCalculationType.MyType;

ILeaveFactoryCategory factoryMock = MockRepository.GenerateMock<ILeaveFactoryCategory >();

factoryMock.Expect(f => f.GetCategory(Arg<LeaveCalculationType>.Is.Equal(expectedCalculationType)).Returns(expectedCalculator);

var proRataClass = new ProRata(factoryMock);
var availableLeaveCount = proRataClass.Calculate(employee, systemDateTime.Now.Date, leaveCount);

factoryMock.VerifyAllExpectations();

This code verifies that factory was used not the result of calculation. If you want to test results it's better to use Stub method instead of Expect and verify calculation result instead of expected behavior.

Strategy pattern with Factory class Unit testing

1 Answers1