dash_threaded example

Start a dash application in a thread, close the server in teardown.

In this example we count the number of times a callback method is called each time a clicked is called and assert the text output of a callback by using wait_for_text_to_equal().

import dash
from dash.dependencies import Output, Input
from dash.exceptions import PreventUpdate

import dash_html_components as html

from pytest_dash import wait_for

def test_application(dash_threaded):
    # The selenium driver is available on the fixture.
    driver = dash_threaded.driver
    app = dash.Dash(__name__)
    counts = {'clicks': 0}

    app.layout = html.Div([
        html.Div('My test layout', id='out'),
        html.Button('click me', id='click-me')
    ])

    @app.callback(
        Output('out', 'children'),
        [Input('click-me', 'n_clicks')]
    )
    def on_click(n_clicks):
        if n_clicks is None:
            raise PreventUpdate

        counts['clicks'] += 1
        return 'Clicked: {}'.format(n_clicks)

    dash_threaded(app)

    btn = wait_for.wait_for_element_by_css_selector(driver, '#click-me')
    btn.click()

    wait_for.wait_for_text_to_equal(driver, '#out', 'Clicked: 1')
    assert counts['clicks'] == 1