Using import_app from dash.testing results in DuplicateCallbackOutput

I have a plotly dash app defined in 2 files:

from flask import Flask
import dash
import dash_bootstrap_components as dbc

server = Flask(__name__)

app = dash.Dash(name='MYAPP', external_stylesheets=[dbc.themes.BOOTSTRAP])
app.title = 'MYAPP'
app.config.suppress_callback_exceptions = True

import dash_core_components as dcc
import dash_html_components as html
from dash.dependencies import Input, Output
from flask import session

from app import app

srv = app.server

app.layout = html.Div([
    dcc.Location(id='url', refresh=False),

@app.callback(Output('page-content', 'children'),
              [Input('url', 'pathname'),
               Input('url', 'hash'),])
def display_page(p_pathname, p_hash):
    # Some logic to serve different pages 
    # (...)

if __name__ == '__main__':
    app.run_server(processes=1, debug=True, threaded=True)

Now, When I try to run more then one test using import_app,


from dash.testing.application_runners import import_app

def test_scenario_1(dash_duo):
     app = import_app('index')

     dash_duo.wait_for_element_by_id('page-content', timeout=30)

     # do some tests (...)

def test_scenario_2(dash_duo):
     app = import_app('index')

     # do other tests (...)

I get an error on scenario 2:

You have already assigned a callback to the output
with ID "page-content" and property "children". An output can only have
a single callback function. Try combining your inputs and
callback functions together into one function.

How to run these two scenarios without an error? Is this a right approach for Plotly Dash App multiple tests?

I have posted the same issue here: