def METHOD_NAME(self):
    eq = self.assertEqual
    get = self.text.get
    writelines = self.window.writelines
    writelines(('Line 1\n', 'Line 2\n', 'Line 3\n'))
    eq(get('1.0', '1.end'), 'Line 1')
    eq(get('2.0', '2.end'), 'Line 2')
    eq(get('3.0', '3.end'), 'Line 3')
    eq(get('insert linestart', 'insert lineend'), '')