In yonicd/reactor: Unit Testing for Shiny Reactivity

knitr::opts_chunk$set(
  collapse = TRUE,
  comment = "#>",
  fig.path = "man/figures/README-",
  out.width = "100%"
)

library(details)

reactor

When developing Shiny apps there is a lot of reactivity problems that can arise when one reactive or observe element triggers other elements. In some cases these can create cascading reactivity (the horror). The goal of reactor is to diagnose these reactivity problems and then plan unit tests to avert them during development to make development less painful.

Installation

And the development version from GitHub with:

# install.packages("remotes")
remotes::install_github("yonicd/reactor")

Usage

Reactor is a pipeline driven api where the user does not need to learn RSelenium in order to be able to drive their applications

Initializing Reactor

Start by creating a reactor class object

library(reactor)
obj <- init_reactor()
obj

Populating Specifications

You can see it is expecting to be populated by two objects

application: Specifications for the background process that will host the application
driver: Specifications for the webdriver that will interact with the application in the background process

Reactor comes with functions to help you create these specifications

application:
- set_runapp_args() : Assumes that the application is located in a path on the machine and uses shiny::runApp as the function to launch the application
- set_golem_args(): Assumes that the application is a golem package and uses the golem logic to launch the application.
driver:
- set_chrome_driver(): Launches RSelenium with a chrome webdriver
- set_firefox_driver(): Launches RSelenium with a firefox (gecko) webdriver

obj <- obj%>%
  set_runapp_args(
    appDir = system.file('examples/good_app.R',package = 'reactor')
  )%>%
  set_chrome_driver()

```{details, echo = FALSE,details.lang = 'yml',details.summary = 'reactor object'} obj

If you want turn off headless mode you can update the object

```r
obj <- obj%>%
  set_chrome_driver(
     opts = chrome_options(headless = FALSE)
  )

```{details, echo = FALSE, details.lang = 'yml',details.summary = 'reactor object'} obj

### Starting Reactor

Once we have specifications in place we can start reactor using `start_reactor()`. 

```r
obj%>%
  start_reactor()

Interacting with the application

Now that the app is running we can send to the webdriver to interact with the application

set_id_value():
expects an input id and the new value
returns back the reactor object

obj%>%
  set_id_value('n',500)

The user can use the following utility functions to interact and query with an application

Inject:

Inputs
set_id_value(): Sets a value for a shiny input object by id
JavaScript
execute(): Executes a JavaScript call

Query:

Inputs
query_input_names(): Returns names of the shiny input ids
query_input_id(): Returns current values of a shiny input by id
Outputs
query_output_names(): Returns names of the shiny output ids
query_output_id(): Returns current values of a shiny output by id
JavaScript
query(): Returns a value from JavaScript call

Closing Reactor

To safely close reactor and all the child processes use kill_app():

obj%>%
  kill_app()

Pipeline Operations

Because each function is returning the reactor object it is simple to create reactor pipelines.

Reactor will wait for shiny to finish each action before proceeding to the next one.

init_reactor()%>%
  set_runapp_args(
    appDir = system.file('examples/good_app.R',package = 'reactor')
  )%>%
  set_chrome_driver()%>%
  start_reactor()%>%
  set_id_value('n',500)%>%
  set_id_value('n',300)%>%
  kill_app()

Testing Expectations

Finally reactor tests reactivity expectations in a testthat framework using the builtin expect_reactivity() function

init_reactor()%>%
  set_runapp_args(
    appDir = system.file('examples/good_app.R',package = 'reactor')
  )%>%
  set_chrome_driver()%>%
  start_reactor()%>%
  set_id_value('n',500)%>%
  expect_reactivity('hist',1)%>%
  set_id_value('n',200)%>%
  expect_reactivity('hist',2)%>%
  kill_app()