如何对依赖于本地声明的对象行为的ac＃方法进行单元测试？

Question

I have ac# method that is dependent on the return value of a service call that it makes with an object that is locally instantiated. How can I test it without making change to the code. I am aware that dependency injection would have made it testable or passing dependency to out of this method would make it testable, but that is not the case here.

My method looks something like this:

public class Animal
{ 
    int Weight;
    public int CalculateActualWeight()
    {
       var weightFactory = new WeightFactory();
       var weight = Weight + weightFactory.GetEatenAmount();
       return weight;
    }
}

The method to be tested is CalculateActualWeight().

Answer 1

You can fake the returned result of a function using something like Moq. You can set it up (it your test) so that your dependency returns whatever you tell it to return. Then you can test the dependent method knowing what the result of the other method will be.

var mock = new Mock<IYourClass>();
mock.Setup(m => m.Method()).Returns(true);

That will make your Method() always return true so that you can test the other. More info on Moq here.

Answer 2

If you cannot change the production code, the only way to test it would be to write a test that surrounds how the locally instantiated object functions as well.

You could also use self stubbing , but that isn't a recommended practice, and will only work if the object under test has functions that can be mocked to replace what you need.

example:

[Test]
public void Test()
{
    //do stuff so that a "real" new WeightFactory() will return what you want
    //(this will require you to go figure out how the WeightFactory works), 
    //4 is just an example of your desired result
    SetUpSystemSoThatWeightFactoryProduces(4);

    var testAnimal = new Animal();
    testAnimal.Weight = 14;

    Assert.That(testAnimal.CalculateWeight(), Is.EqualTo(18));
}