Take a screenshot of a SwiftUI View in a XCTest - swiftui

Question

I'd like to be able to take an Screenshot of a SwiftUI View in a XCTest.
I've tried things like the hackingwithswifts extension: https://www.hackingwithswift.com/quick-start/swiftui/how-to-convert-a-swiftui-view-to-an-image
However, my use case it slightly different, I need it to run in a XCTest. I've also seen pointfreeco snapshot testing, however, I want to understand why what I've written just produces either a black or empty image.
I've tried using a displayLink to screenshot during a loop, but the image is still empty. I feel I'm missing something fundamental.
Can anyone offer any help? Thank you
import SwiftUI
import XCTest
final class MyTests: XCTestCase {
func test_screenshot_view() throws {
let swiftUIView = Button {
} label: {
Text("Hello, World!")
}
.frame(width: 140, height: 56)
let controller = UIHostingController(rootView: swiftUIView)
let window = UIWindow()
window.rootViewController = controller
let view = controller.view
let targetSize = controller.view.intrinsicContentSize
view!.bounds = CGRect(origin: .zero, size: targetSize)
view!.backgroundColor = UIColor.yellow
UIGraphicsBeginImageContextWithOptions(view!.bounds.size, view!.isOpaque, 0)
view!.drawHierarchy(in: view!.bounds, afterScreenUpdates: true)
let snapshotImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
//snapshotImage is either black or empty
}
}

Answer 1

Just an update, this seems to work, but has some sizing issues:
import SwiftUI
import CoreGraphics
extension View {
func asImage() -> UIImage {
let controller = UIHostingController(rootView: self)
let view = controller.view
let targetSize = controller.view.intrinsicContentSize
let bounds = CGRect(origin: .zero, size: targetSize)
let window = UIWindow(frame: bounds)
window.rootViewController = controller
window.makeKeyAndVisible()
view?.bounds = bounds
view?.backgroundColor = .clear
let image = controller.view.asImage()
return image
}
}
extension UIView {
func asImage() -> UIImage {
let renderer = UIGraphicsImageRenderer(bounds: bounds)
return renderer.image { rendererContext in
layer.render(in: rendererContext.cgContext)
}
}
}