fbs PyQt5 unable to write file

main.py

from fbs_runtime.application_context.PyQt5 import ApplicationContext
from PyQt5.QtWidgets import (QMainWindow, QLabel, QPushButton,
                             QWidget, QStackedWidget)
import sys
import os
import os.path as op


class AppContext(ApplicationContext):
    def run(self, path):
        exp = Test(500, 500, path)
        exp.show()
        return self.app.exec_()


class Test(QMainWindow):

    def __init__(self, width, height, path):
        super().__init__()
        self.path = path
        self.setGeometry(0, 0, width, height)
        self.stack = QStackedWidget(self)
        self.setCentralWidget(self.stack)
        self.stack.addWidget(self.screen1())  # 0
        self.stack.addWidget(self.screen2())  # 1

    # SCREENS
    def screen1(self):
        screen1 = QWidget()
        button = QPushButton('start', screen1)
        button.pressed.connect(self.test)
        return screen1

    def screen2(self):
        screen2 = QWidget()
        screen2.label = QLabel(self.path, screen2)
        return screen2

    def test(self):
        self.stack.setCurrentIndex(1)
        with open(op.join('/Applications', 'test.txt', 'w')) as f:
            f.write('test')


if __name__ == '__main__':
    path = os.getcwd()
    appctxt = AppContext()
    exit_code = appctxt.run(path)
    sys.exit(exit_code)