How to create a Widget using .ui file?

I'd like to create a widget inside a MainWindow that gets its design from a file created with QtDesigner.

• the .ui file I created is test.ui
• I have a MainWindow instance inheriting from QMainWindow that will create a stacked widget with many widgets inside it. For simplicity in this example, it will create just a widget as central widget.
• The My Widget instance inside the MainWindow is the one that has to grab its design from the .ui file

As it is, the application shows a blank window

Here is the code:

from PySide2.QtWidgets import QMainWindow, QApplication, QDesktopWidget, QWidget
from PySide2.QtCore import QCoreApplication, Qt

from PySide2.QtUiTools import QUiLoader
from PySide2.QtCore import QFile

class MyWidget(QWidget):
    def __init__(self, parent=None):        
        super(MyWidget, self).__init__(parent)

    ui_file = QFile("test.ui")
    ui_file.open(QFile.ReadOnly)

    loader = QUiLoader()
    window = loader.load(ui_file)
    ui_file.close()


class MainWindow(QMainWindow):

    def __init__(self):
        super(MainWindow, self).__init__()
        self.ui_dim_percentage = 70/100
        self.initUI()

    def initUI(self):
        self.center()

        self.home_widget = MyWidget(self)
        self.setCentralWidget(self.home_widget)

        self.show()

    def center(self): # resizes the UI to a percentage of the screen and centers the widget

        screen_size = QDesktopWidget().screenGeometry()
        self.resize(screen_size.width()*self.ui_dim_percentage, screen_size.height()*self.ui_dim_percentage)

        qr = self.frameGeometry()
        cp = QDesktopWidget().availableGeometry().center()
        qr.moveCenter(cp)
        self.move(qr.topLeft())


def main():

    app = QApplication(sys.argv)
    ex = MainWindow()
    sys.exit(app.exec_())


if __name__ == '__main__':
    main()

How should I correct the code?