pytest-dash 1.0.0

pytest fixtures to run dash app.

pytest-dash

Pytest fixtures for dash.

Install

$ pip install pytest-dash

Fixtures

dash_threaded

Start a dash instance in a thread, stop the server in teardown. Use this if you need to count how many times a callback was fired.

import dash

import dash_html_components as html

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

from pytest_dash.utils import wait_for_element_by_css_selector
from pytest_dash.utils import wait_for_text_to_equal

def test_app(dash_threaded, selenium):
    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_element_by_css_selector(selenium, '#click-me')
    btn.click()
    
    wait_for_text_to_equal(selenium, '#out', 'Clicked: 1')
    assert counts['clicks'] == 1

dash_subprocess

experimental

Start an app instance contained in a module with waitress-serve in a subprocess. Kill the process in teardown.

from pytest_dash.utils import wait_for_text_to_equal

def test_subprocess(dash_subprocess, selenium):
    dash_subprocess('test_apps.simple_app')

    value_input = selenium.find_element_by_id('value')
    value_input.clear()
    value_input.send_keys('Hello dash subprocess')

    wait_for_text_to_equal(selenium, '#out', 'Hello dash subprocess')

Utils

Helper methods.

• wait_for_element_by_css_selector(driver, selector, timeout=10),
• wait_for_text_to_equal(driver, selector, text, timeout=10)
• import_app(app_file), Load a file with runpy, return the app instance.

More resources

• Dash user guide
• Pytest