使用Xamarin.UITest时如何伪造后台活动

Question

I'm creating a Xamarin.Forms App and want to use UITest to test the correct behavior of my View. The View does not only react on user input like button click or the like. Instead there are background operations which should lead to changes in the View like hiding one element and showing another element at this point. Another example is filling a ListView with elements which would be produced by a background operation. These changes would be made on the ViewModel whose properties are bound to the View. Now I want to simulate the background operation and test that my View behaves correctly. But I can not manipulate my ViewModel while in the UITest project because I cannot reference Xamarin.Forms in the Test class. It seems like it isn't intended to test the application this way. The whole app is a black box for the UITest and you can only interact through mouse and keyboard input with it. How can I access internals of my app, the corresponding ViewModel for example. I already searched for this problem but found nothing. Maybe I'm searching in the wrong direction. Any help would be highly appreciated.

Answer 1

You can use a back door to access a method in a platform project, and from there you should be able to access Forms code since your app project references the Forms core project. See: https://developer.xamarin.com/guides/testcloud/uitest/working-with/backdoors/

Create backdoor method in Android project:

In MainActivity:

[Export("MyBackdoorMethod")]
// Can optionally take a parameter of string, int, or bool.
// Can optionally return  string or Java.Lang.String. 
public void MyBackdoorMethod() 
{
    // In through the backdoor - do some work.
}

To call the Android backdoor method from a test:

app.Invoke("MyBackdoorMethod");

Create backdoor method in iOS project:

In AppDelegate:

[Export("myBackdoorMethod:")] // notice the colon at the end of the method name
// Must take an NSString and return an NSString.
public NSString MyBackdoorMethod(NSString value)
{
    // In through the backdoor - do some work.
}

To call the iOS backdoor method from a test:

app.Invoke("myBackdoorMethod:", "the value");

More details at the link, but this should suffice to get one going.

Answer 2

On iOS, you already have a method to achieve it called SendAppToBackground . You can also pass the time to be in the background with a TimeSpan object (wiki info) . However, you cannot achieve this on Android.

Here is a sample to use it on your UITest project:

public void SendAppToBackground(IApp app, TimeSpan timeSpan)
{
    if (OnAndroid)
    {
        return;
    }

    ((iOSApp)app).SendAppToBackground(timeSpan);

    app.Screenshot("Return from background state.");

    return this;
}