AVCapturePhotoOutput didFinishProcessingPhoto not getting called

Question

I am trying to capture an image using AVCapturePhotoOutput and AVCaptureSession, my code is as follows (running it though an XCTest):

func testCapture() {
    let expectation = expectation(description: "Camera")
    let captureSession = AVCaptureSession()
    let videoDevice = AVCaptureDevice.default(for: .video)

    // Create the capture device.
    let videoDeviceInput = try! AVCaptureDeviceInput(device: videoDevice!)
    guard captureSession.canAddInput(videoDeviceInput) else {
        assert(false)
        return
    }
    captureSession.addInput(videoDeviceInput)

    let photoOutput = AVCapturePhotoOutput()
    guard captureSession.canAddOutput(photoOutput) else {
        assert(false)
        return
    }
    captureSession.sessionPreset = .photo
    photoOutput.isHighResolutionCaptureEnabled = true

    // Add the output.
    captureSession.addOutput(photoOutput)
    
    // Open the camera.
    captureSession.startRunning()

    // Create callback.
    let delegate = Delegate({ photo in
        print("Success")
        expectation.fulfill()
    })
    
    let settings = AVCapturePhotoSettings()
    photoOutput.capturePhoto(with: settings, delegate: delegate)
    self.wait(for: [expectation], timeout: 30)
}

And my Delegate object is:

private class Delegate: NSObject, AVCapturePhotoCaptureDelegate {
    let callback: (AVCapturePhoto) -> Void
    init(_ callback: @escaping (AVCapturePhoto) -> Void) {
        self.callback = callback
    }

    func photoOutput(_ output: AVCapturePhotoOutput, didFinishProcessingPhoto photo: AVCapturePhoto, error: Error?) {
        print("Did finish processing photo: \(photo) error: \(error)")
        self.callback(photo)
    }
    func photoOutput(_ output: AVCapturePhotoOutput, willBeginCaptureFor resolvedSettings: AVCaptureResolvedPhotoSettings) {
        print("Will begin capture")
    }
    func photoOutput(_ output: AVCapturePhotoOutput, willCapturePhotoFor resolvedSettings: AVCaptureResolvedPhotoSettings) {
        print("Will capture photo")
    }
    func photoOutput(_ output: AVCapturePhotoOutput, didFinishCaptureFor resolvedSettings: AVCaptureResolvedPhotoSettings, error: Error?) {
        print("didFinishCaptureFor")
    }
    func photoOutput(_ output: AVCapturePhotoOutput, didFinishRecordingLivePhotoMovieForEventualFileAt outputFileURL: URL, resolvedSettings: AVCaptureResolvedPhotoSettings) {
        print("didFinishRecordingLivePhotoMovieForEventualFileAt")
    }
    func photoOutput(_ output: AVCapturePhotoOutput, didCapturePhotoFor resolvedSettings: AVCaptureResolvedPhotoSettings) {
        print("Did capture image")
    }
    func photoOutput(_ output: AVCapturePhotoOutput, didFinishProcessingLivePhotoToMovieFileAt outputFileURL: URL, duration: CMTime, photoDisplayTime: CMTime, resolvedSettings: AVCaptureResolvedPhotoSettings, error: Error?) {
        print("Did finish processing live")
    }
    func photoOutput(_ output: AVCapturePhotoOutput, didFinishProcessingPhoto photoSampleBuffer: CMSampleBuffer?, previewPhoto previewPhotoSampleBuffer: CMSampleBuffer?, resolvedSettings: AVCaptureResolvedPhotoSettings, bracketSettings: AVCaptureBracketedStillImageSettings?, error: Error?) {
        print("Did finish processing2")
    }
    func photoOutput(_ output: AVCapturePhotoOutput, didFinishProcessingRawPhoto rawSampleBuffer: CMSampleBuffer?, previewPhoto previewPhotoSampleBuffer: CMSampleBuffer?, resolvedSettings: AVCaptureResolvedPhotoSettings, bracketSettings: AVCaptureBracketedStillImageSettings?, error: Error?) {
        print("Did finish processing raw")
    }
}

Running the code produces the following output:

Will begin capture
Will capture photo
Did capture image

It's missing the call to didFinishProcessingPhoto.

Any idea for what might be the cause?