knitr::opts_chunk$set( collapse = TRUE, comment = "#>" ) library(shinytest2) library(shiny)
{shinytest2}
Most people will use {shinytest2}
with the plug and play
record_test()
app, which is very convenient if you are not familiar
with JavaScript. Under the hood, record_test()
generates an R script
composed of a series of directed instructions that manipulates the app
to automate testing on CI/CD environments.
Monkey testing, a type of testing where random inputs are used to test
the behavior of an app, is widely used by web developers to check
application robustness, particularly in apps with a large number of
inputs. The goal is ultimately to try to break the app by triggering
unexpected combinations. Most available libraries are JS-based such as
gremlins.js, traditionally
combined with JS-based global testing libraries like
Puppeteer, but can work with {shinytest2}
as
well.
In this vignette we'll provide a more thorough overview of the
AppDriver
R6 class (extending on the concepts covered in the Testing
in depth article), which allows the developer to
programmatically control the app. We'll see how we can seamlessly
benefit from gremlins.js with only few lines of code.
We consider a simple app composed of a slider and a plot output:
ui <- fluidPage( sliderInput("obs", "Number of observations:", min = 0, max = 1000, value = 500 ), plotOutput("distPlot") ) # Server logic server <- function(input, output) { output$distPlot <- renderPlot({ hist(rnorm(input$obs)) }) } # Complete app with UI and server components shinyApp(ui, server)
The driver may be initialized with:
headless_app <- AppDriver$new( app_dir = "<PATH_TO_APP>", name = "monkey-test", shiny_args = list(port = 3515) )
Note the shiny_args
slot allowing you to pass custom options to
shiny::runApp()
such as the port, which might be useful if your
organization restricts port number. load_timeout
defaults to 10s and
20s locally and during CI/CD, respectively. Therefore, if your app takes
longer to launch, you can change this value. Keep in mind that an app
taking more than 20s to launch is generally under-optimized and would
require specific care such as profiling and refactoring.
AppDriver starts a Chrome-based headless browser. If you need specific
flags
that are not available by default in {shinytest2}
, you can pass them
before instantiating the driver:
chromote::set_chrome_args( c( chromote::default_chrome_args(), # Custom flags: see https://peter.sh/experiments/chromium-command-line-switches/ ) )
Some flags are considered by default, particularly --no-sandbox
, which
is applied only on CI/CD, as Chrome won't start without it.
If you run this script locally, you may add view = TRUE
to open the
Chrome Devtools, which will significantly ease the testing calibration.
I highly recommend creating the test protocol locally and then moving to
CI/CD later when all bugs are fixed.
In the below figure, the application is shown on the left side panel. The top-right side panel shows the DOM elements (default) and the bottom-right side panel displays the JavaScript console output.
knitr::include_graphics("images/gremlins-start.png")
The next steps consist of injecting the gremlins.js dependency in the DOM so that we can unleash the horde.
The easiest way to inject gremlins.js is to call:
headless_app$run_js(" let s = document.createElement('script'); s.src = 'https://unpkg.com/gremlins.js'; document.body.appendChild(s); ")
This creates a <script>
tag pointing to the correct Content Delivery
Network (CDN), an optimized server to store libraries, and inserts it at
the end of the body.
To test whether everything worked well, we can dump the DOM and look for
the scripts. We can find gremlins.js by calling
typeof window.gremlins
, which returns an object:
headless_app$get_html("script", outer_html = TRUE) headless_app$get_js("typeof window.gremlins")
You may instead see undefined
returned. This is generally because the
JS code is blocked by the network. If this is the case, consider
injecting gremlins.js locally, as explained in the next section.
knitr::include_graphics("images/gremlins-inject.png")
You can store and serve a local copy of the gremlins.js script with
shiny::addResourcePath()
, assuming gremlins.js
is in
inst/js/gremlins.min.js
. You can accomplish this by adding the
following code to the app.R
file:
shiny::addResourcePath("gremlins", "inst/js/gremlins.min.js")
We can subsequently inject the gremlins in the DOM and check whether everything worked as expected:
headless_app$run_js(" let s = document.createElement('script'); s.src = './gremlins/gremlins.min.js'; document.body.appendChild(s); ") headless_app$get_html("script", outer_html = TRUE) headless_app$get_js("typeof window.gremlins")
The workflow is rather simple:
gremlins.createHorde()
.horde.unleash();
.const horde = gremlins.createHorde(); horde.unleash();
createHorde()
accepts many species of gremlins capable of handling
various events such as clicks, touch, form filling, scrolling, typing,
and more, as described in the gremlins.js
documentation.
We don't recommend using the scroller,
which sometimes
crashes the Chrome
instance.
If your plots rely on random elements, such as rnorm
, it is best
practice to set up a seed using set.seed()
. By default, all species
will attack in random order with a delay of 10 ms between each event.
You can also control the attack strategy to fine tune the global
behavior. If you want more control over what your gremlins species
should be doing, you can define a custom species.
In the following, we run the most basic monkey test configuration:
headless_app$run_js("gremlins.createHorde().unleash();")
The result is shown in the GIF below:
knitr::include_graphics("images/gremlins-attack.gif")
Does it really makes sense to invoke all species given we only have a slider? Absolutely not! We can use the following code to test only the slider input.
knitr::include_graphics("images/gremlins-slider-handle.png")
The best species to perform this task is the toucher
, which is able to
randomly move the slider input. The documentation specifies many events
such as tap, doubletap, gesture and multi-touch. It seems more relevant
to apply only gesture, consisting of dragging the slider on the x-axis
(note: gesture also considers the y-axis, which does not make sense for
the slider. While this is a gremlins.js limitation, it won't prevent our
test from running).
We target the slider handle by its class, irs-handle single,
to ensure
we don't touch any other element. We also increase the number of maximum
touches from 2 to 200. Note the HTML inspector, which allows us to
seamlessly inspect and extract any class or id. The log parameter
enables logging in the JavaScript console:
const customToucher = gremlins.species.toucher({ // which touch event types will be triggered touchTypes: ['gesture'], // Touch only if element has class irs-handle single canTouch: (element) => element.className === 'irs-handle single', log: true, maxTouches: 200 });
We can create our custom horde and disable the FPS and Alert mogwais gremlins since they are not relevant to our case study:
const horde = gremlins.createHorde({ species: [customToucher], mogwais: [gremlins.mogwais.gizmo()] });
As unleash
is a promise, we can execute a function right after it,
in order to check whether the script ran as expected.
horde
.unleash()
.then(() => {
console.log('Gremlins test success')
});
If you are running on CI/CD and can't see the Chrome Devtools, you can
still display the logs. The console.log
output will be captured by the
{shinytest2}
logs with headless_app$get_logs()
allowing you to debug
and refine the monkey testing script.
knitr::include_graphics("images/gremlins-logs.png")
As monkey testing lasts about 10s, you often want to take a screenshot of the ongoing attack:
headless_app$run_js(" const customToucher = gremlins.species.toucher({ // which touch event types will be triggered touchTypes: ['gesture'], // Touch only if element has class irs-handle single canTouch: (element) => element.className === 'irs-handle single', log: true, maxTouches: 200 }); gremlins.createHorde({ //randomizer: new gremlins.Chance(1234), // repeatable species: [customToucher], mogwais: [gremlins.mogwais.gizmo()] }).unleash().then(() => { console.log('Gremlins test success') }); ") Sys.sleep(3) headless_app$get_screenshot("gremlins.png")
knitr::include_graphics("images/gremlins-attack-refined.gif")
Should you run multiple attacks, it is always good practice to reset Shiny inputs between attacks, or even close the current headless app and restart a new session:
headless_app$set_inputs(obs = 500)
If you run on CI/CD, don't forget to clean the session after tests are
completed, particularly if you set the shiny.port
option, as you can't
have 2 apps running on the same port:
headless_app$stop()
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