如何从数据类型为字典的只读属性模拟或存根方法？

Question

I am starting out on the rhino mocks and ran into a compounded problem.

I have a dependency on a class AppDefaults which has a readonly property "Properties" with datatype of Dictionary.

My Class under test uses the result of a Dictionary function .ContainsKey() which returns a boolean.

MyAppDefaultsInstance.Properties.ContainsKey("DefaultKey")

I only got around this by creating a public virtual function on the class under test to wrap the .Contains function. But is there a way to Mock or stub .ContainsKey result without having a wrapper to mock it?

Example Code:

    public class AppDefaults
{

    public readonly IDictionary<String, String> Properties = new Dictionary<string, string>();

    public AppDefaults()
    {
        LoadProperties();
    }

    private void LoadProperties()
    {
        //load the properties;
    }

    public virtual int GetPropertyAsInt(string propertyKey)
    {
        return XmlConvert.ToInt32(Properties[propertyKey]);
    }

}


public class DefaultManager
{
    AppDefaults _appsDefault;
    public int TheDefaultSize
    {
        get
        {
            int systemMax;
            int currentDefault = 10;

            if (_appsDefault.Properties.ContainsKey("DefaultKey"))
            {
                systemMax = _appsDefault.GetPropertyAsInt("DefaultKey");
            }
            else
            {
                systemMax = currentDefault;
            }

            return systemMax;
        }
    }

    public DefaultManager(AppDefaults appDef) {
        _appsDefault = appDef;
    }
}

[TestClass()]
public class DefaultManagerTest
{

    [TestMethod()]
    public void TheDefaultSizeTest()
    {
        var appdef = MockRepository.GenerateStub<AppDefaults>();

        appdef.Expect(m => m.Properties.ContainsKey("DefaultKey")).Return(true);

        appdef.Stub(app_def => app_def.GetPropertyAsInt("DefaultKey")).Return(2);

        DefaultManager target = new DefaultManager(appdef); 

        int actual;
        actual = target.TheDefaultSize;
        Assert.AreEqual(actual, 2);
    }
}

Answer 1

Instead of mocking the .ContainsKey method why don't you just populate the dictionary with some predefined value for the test:

// arrange
var appDef = new AppDefaults();
appDef.Properties["DefaultKey"] = "2";

// act
var target = new DefaultManager(appDef); 

// assert
Assert.AreEqual(target.TheDefaultSize, 2);

Answer 2

I would not expose

AppDefaults.Properties

field. Instead of that you can add a method like

GetProperty(string key) 

to AppDefaults (that will return the key if it exists and so on) and mock it's result in your unit test. Mocked method will return the value that you will check target.TheDefaultSize against.