Testing with Launchers and Choosers

Unit testing code that uses a launcher or chooser directly is a challenge because both types of tasks cause your app to be deactivated. No means to abstract launchers or choosers exists out-of-the-box; therefore, I have included in the downloadable sample code a set of classes that do just that.

Just as we abstracted the built-in LicenseInformation class in the previous section, here we do the same with the MarketDetailTask. The MarketDetailTask is a launcher which, when shown, takes the user to the built-in marketplace application. When showing the MarketplaceDetailTask during a debugging session, the native marketplace application displays an error because it expects an app with an id that has been officially published to the marketplace.

The main issue, however, is that when the MarketplaceDetailTask is shown, it deactivates the app. Thus, it makes sense to abstract the task as in the LicenseInformation class in the previous section.

The abstracted custom interface for the MarketplaceDetailTask is named IMarketDetailTask and contains a single method named Show. There are two implementations of this interface. The first, named MarketplaceDetailTaskAdapter, calls the Show method of a built-in MarketplaceDetailTask instance when its own Show method is called, as shown in the following excerpt:

Click here to view code image

public class MarketplaceDetailTaskAdapter : IMarketplaceDetailTask
{
    public void Show()
    {
        var marketplaceDetailTask = new MarketplaceDetailTask();
        marketplaceDetailTask.Show();
    }
}

The unit test compatible implementation of the IMarketplaceDetailTask is called MockMarketplaceDetailTask and allows a specified Action to be invoked when the Show method is called:

Click here to view code image

public class MockMarketplaceDetailTask : IMarketplaceDetailTask
{
    readonly Action action;

    public MockMarketplaceDetailTask(Action action)
    {
        this.action = action;
    }

    public void Show()
    {
        if (action != null)
        {
            action();
        }
    }
}

The ChatClientViewModel class contains an ICommand named BuyCommand, which, when executed, retrieves the IMarketplaceDetailTask from the IoC container and calls its Show method. BuyCommand is initialized in the viewmodel’s constructor, as shown:

Click here to view code image

buyCommand = new DelegateCommand(
    obj =>
    {
        var marketplaceDetailTask
            = Dependency.Resolve<IMarketplaceDetailTask>();
        marketplaceDetailTask.Show();
    });

When the BuyCommand is executed, it causes the IMarketDetailTask instance to be resolved using the static Dependency.Resolve method. Recall that a particular implementation of the IMarketDetailTask is registered according to the selected build configuration, as described in the earlier section “A Custom IoC Container and DI Framework.” If the build is using a Release configuration, an instance of the MarketplaceDetailTaskAdapter is resolved, which, in turn, causes an instance of the built-in MarketplaceDetailTask to be shown. Conversely, if the build is using a Debug configuration, the MockMarketplaceDetailTask is used, which does not disrupt unit testing or any manual ad hoc testing.