---
title: "Monkey testing"
author: David Granjon
output: rmarkdown::html_vignette
vignette: >
  %\VignetteIndexEntry{Monkey testing}
  %\VignetteEncoding{UTF-8}
  %\VignetteEngine{knitr::rmarkdown}
---

```{r, include = FALSE}
knitr::opts_chunk$set(
  collapse = TRUE,
  comment = "#>"
)
library(shinytest2)
library(shiny)
```

# Monkey (headless) testing with `{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](https://github.com/marmelab/gremlins.js), traditionally
combined with JS-based global testing libraries like
[Puppeteer](https://pptr.dev/), 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](in-depth.html) 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.


## Initialize the driver

We consider a simple app composed of a slider and a plot output:

``` r
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:

``` r
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](https://peter.sh/experiments/chromium-command-line-switches/)
that are not available by default in `{shinytest2}`, you can pass them
before instantiating the driver:

``` r
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.

```{r echo=FALSE, eval=TRUE, out.width='100%', fig.align='center'}
knitr::include_graphics("images/gremlins-start.png")
```

## Injecting gremlins.js

The next steps consist of injecting the gremlins.js dependency in the
DOM so that we can unleash the horde.

### Easy way

The easiest way to inject gremlins.js is to call:

``` r
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:

``` r
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.

```{r echo=FALSE, eval=TRUE, out.width='100%', fig.align='center'}
knitr::include_graphics("images/gremlins-inject.png")
```

### Local way

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:

``` r
shiny::addResourcePath("gremlins", "inst/js/gremlins.min.js")
```

We can subsequently inject the gremlins in the DOM and check whether
everything worked as expected:

``` r
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")
```

## Unleash the horde

### A bit about gremlins.js

The workflow is rather simple:

-   We create the horde with `gremlins.createHorde()`.
-   We run the monkey test with `horde.unleash();`.

``` js
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](https://github.com/marmelab/gremlins.js#advanced-usage).

We don't recommend using the `scroller,` which sometimes
[crashes](https://github.com/rstudio/shinytest2/issues/117) 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.

### Practice

#### Blind run

In the following, we run the most basic monkey test configuration:

``` r
headless_app$run_js("gremlins.createHorde().unleash();")
```

The result is shown in the GIF below:

```{r echo=FALSE, eval=TRUE, out.width='100%', fig.align='center'}
knitr::include_graphics("images/gremlins-attack.gif")
```

#### Optimized testing

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.

```{r echo=FALSE, eval=TRUE, out.width='100%', fig.align='center'}
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:

``` 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
});
```

We can create our custom horde and disable the FPS and Alert mogwais
gremlins since they are not relevant to our case study:

``` js
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.

``` js
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.

```{r echo=FALSE, eval=TRUE, out.width='100%', fig.align='center'}
knitr::include_graphics("images/gremlins-logs.png")
```

As monkey testing lasts about 10s, you often want to take a screenshot
of the ongoing attack:

``` r
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")
```

```{r echo=FALSE, eval=TRUE, out.width='100%', fig.align='center'}
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:

``` r
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:

``` r
headless_app$stop()
```
