flask test 400 error page does not pass but it is working

I m redirecting 403 error to a personal page. It works fine but test does not pass. I ve other tests that works fine.

this is my code for test: class TestErrorPages(TestBase):

def test_403_forbidden(self):
    # create route to abort the request with the 403 Error
    @self.app.route('/403')
    def forbidden_error():
        abort(403)

Test are not passed and error is:

Traceback (most recent call last):
  File "/usr/local/Cellar/python/3.7.7/Frameworks/Python.framework/Versions/3.7/lib/python3.7/unittest/case.py", line 59, in testPartExecutor
    yield
  File "/usr/local/Cellar/python/3.7.7/Frameworks/Python.framework/Versions/3.7/lib/python3.7/unittest/case.py", line 628, in run
    testMethod()
  File "/Users/xxxxx/PycharmProjects/setup/test.py", line 184, in test_403_forbidden
    self.assertTrue("403 Error" in response.data)
TypeError: a bytes-like object is required, not 'str'

Where is my error ?