testServer function

Reactive testing for Shiny server functions and modules

A way to test the reactive interactions in Shiny applications. Reactive interactions are defined in the server function of applications and in modules.

testServer(app = NULL, expr, args = list(), session = MockShinySession$new())

Arguments

• app: A server function (i.e. a function with input, output, and session), or a module function (i.e. a function with first argument id that calls moduleServer().

  You can also provide an app, a path an app, or anything that as.shiny.appobj() can handle.

• expr: Test code containing expectations. The objects from inside the server function environment will be made available in the environment of the test expression (this is done using a data mask with rlang::eval_tidy()). This includes the parameters of the server function (e.g. input, output, and session), along with any other values created inside of the server function.

• args: Additional arguments to pass to the module function. If app is a module, and no id argument is provided, one will be generated and supplied automatically.

• session: The MockShinySession object to use as the reactive domain . The same session object is used as the domain both during invocation of the server or module under test and during evaluation of expr.

Examples

# Testing a server function  ----------------------------------------------
server <- function(input, output, session) {
  x <- reactive(input$a * input$b)
}

testServer(server, {
  session$setInputs(a = 2, b = 3)
  stopifnot(x() == 6)
})

# Testing a module --------------------------------------------------------
myModuleServer <- function(id, multiplier = 2, prefix = "I am ") {
  moduleServer(id, function(input, output, session) {
    myreactive <- reactive({
      input$x * multiplier
    })
    output$txt <- renderText({
      paste0(prefix, myreactive())
    })
  })
}

testServer(myModuleServer, args = list(multiplier = 2), {
  session$setInputs(x = 1)
  # You're also free to use third-party
  # testing packages like testthat:
  #   expect_equal(myreactive(), 2)
  stopifnot(myreactive() == 2)
  stopifnot(output$txt == "I am 2")

  session$setInputs(x = 2)
  stopifnot(myreactive() == 4)
  stopifnot(output$txt == "I am 4")
  # Any additional arguments, below, are passed along to the module.
})