Possible to bring the app from background to foreground?

Update for Xcode 9: Starting in Xcode 9, you can now simply call activate() on any XCUIApplication.

let myApp = XCUIApplication()
myApp.activate() // bring to foreground

https://developer.apple.com/documentation/xctest/xcuiapplication/2873317-activate

Yes, it is. But, you'll need XCUIElement's private headers (which are available via header dump from Facebook here). In order to foreground the app, you need to call resolve which I believe resolves the element's query (which for applications means foregrounding the app).

For Swift, you'll have to import the XCUIElement.h into your bridging header. For Objective-C you'll just need to import XCUIElement.h.

With the app backgrounded:

Swift:

XCUIApplication().resolve()

Objective-C

[[XCUIApplication new] resolve];

If this is the only functionality you need, you could just write a quick ObjC category.

@interface XCUIElement (Tests)
- (void) resolve;
@end

If you need to launch / resolve another app. Facebook has an example of that here by going through the Springboard.