test_interval.py

import dash
from dash.testing import wait
from dash.dependencies import Input, Output
import dash_core_components as dcc
import dash_html_components as html
import time


def test_intv001_interval(dash_dcc):
    app = dash.Dash(__name__)
    app.layout = html.Div(
        [
            html.Div(id="output"),
            dcc.Interval(id="interval", interval=1, max_intervals=2),
        ]
    )

    @app.callback(Output("output", "children"), [Input("interval", "n_intervals")])
    def update_text(n):
        return "{}".format(n)

    dash_dcc.start_server(app)

    time.sleep(5)

    dash_dcc.wait_for_text_to_equal("#output", "2")
    assert dash_dcc.get_logs() == []


def test_intv002_restart(dash_dcc):
    app = dash.Dash(__name__)
    app.layout = html.Div(
        [
            dcc.Interval(id="interval", interval=100, n_intervals=0, max_intervals=-1,),
            html.Button("Start", id="start", n_clicks_timestamp=-1),
            html.Button("Stop", id="stop", n_clicks_timestamp=-1),
            html.Div(id="output"),
        ]
    )

    @app.callback(
        Output("interval", "max_intervals"),
        [Input("start", "n_clicks_timestamp"), Input("stop", "n_clicks_timestamp"),],
    )
    def start_stop(start, stop):
        if start < stop:
            return 0
        else:
            return -1

    @app.callback(Output("output", "children"), [Input("interval", "n_intervals")])
    def display_data(n_intervals):
        return "Updated {}".format(n_intervals)

    dash_dcc.start_server(app)

    wait.until(lambda: dash_dcc.find_element("#output").text != "Updated 0", 3)
    dash_dcc.find_element("#stop").click()
    time.sleep(2)

    text_now = dash_dcc.find_element("#output").text
    time.sleep(2)
    text_later = dash_dcc.find_element("#output").text

    assert text_now == text_later

    dash_dcc.find_element("#start").click()

    wait.until(lambda: dash_dcc.find_element("#output").text != text_later, 3)

    assert dash_dcc.get_logs() == []