我可以模拟无法实例化的对象吗？

Question

I am using some COM library in my C# which is bound to particular hardware and doesn't work without it. On development/testing computer I don't have that hardware. The method which is using library looks like this:

using HWSysManagerLib;
bool ProcessBias(HWSysManager systemManager, string hwPath)
{
    int handle = systemManager.OpenConfiguration(hwPath);
    ...
    // some magic goes here
    // return result
}

The question is, can I mock HWSysManager for test method and how? There are few methods only in HWSysManager and it wouldn't be problem to simulate their functionality for test. A tiny example would be great on how to mock it, if it's possible at all.

Answer 1

You can use the adapter pattern here.

Create an interface named IHWSysManager

public interface IHWSysManager
{
    int OpenConfiguration(string hwPath);
}

The real implementation class just delegates the work to the library:

public class HWSysManagerImpl : IHWSysManager
{
    private HWSysManager _hwSysManager; //Initialize from constructor

    public int OpenConfiguration(string hwPath)
    {
        return _hwSysManager.openConfiguration(hwPath);
    }
}

Use the interface in your code like this:

bool ProcessBias(IHWSysManager systemManager, string hwPath)
{
    int handle = systemManager.OpenConfiguration(hwPath);
    ...
    // some magic goes here
    // return result
}

Now you can mock your IHWSysManager interface with mock frameworks or you can create a stub class yourself.

Answer 2

You can use Typemock Isolator for faking HWSysManager.

For your example, you can do the following:

var fakeManager = Isolate.Fake.Instance<HWSysManager>();

Isolate.WhenCalled(() => fakeManager.OpenConfiguration("")).WillReturn(0);

And then, you can pass this faked manager to ProcessBias(IHWSysManager systemManager, string hwPath) as an argument.

As you said, you can simulate a few methods from IHWSysManager. So, me advice is to set up the behavior of this manager's methods using DoInstead():

Isolate.WhenCalled(() => fakeManager.OpenConfiguration("")).DoInstead(
    context =>
    {
        //Your simulation
    });

You can look here for more information. I think, it can be really useful for you.

Answer 3

I suppose you should create HWSysManager(or some other name) class to your Mock cases, add there some wanted methods and then mock them. For example:

    class HWSysManager
    {
        public virtual int ExampleReturnIntMethod(int a)
        {
            var someInt = 0;
            return someInt;
        }

and then setup:

    public void TestMethod()
    {
        Mock<HWSysManager> hwSysManager = new Mock<HWSysManager>();
        hwSysManager.Setup(x => x.ExampleReturnInMethod(It.IsAny<int> ())).Returns(10); //if parameter is any of int, return 10 in this case
    }

Then to use your Mocked object just use the 'object' property:

 var hwSysInstance = hwSysManager.Object;
 var result = hwSysInstance.ExampleReturnInMethod(2); //result will be 10 in this case - as we have mocked

In case above your methods/properties have to be virtual.

You can use interfaces also, in your case:

    public interface HwsysManager
    {
        int OpenConfiguration(string hwPath);
    }

     public void TestMethod()
    {
      Mock<HwsysManager> hwsysManager = new Mock<HwsysManager>();

      hwsysManager.Setup(x => x.OpenConfiguration(It.IsAny<string>())).Returns(10);
    }

All features of this Mock library are described here: https://github.com/Moq/moq4/wiki/Quickstart