promise_test.R

library(promises)
library(future)
library(shiny)
library(testthat)

plan(multiprocess)

adderModule <- function(id, sleepFor, n) {
  moduleServer(id, function(input, output, session) {
    output$sum <- renderText({
      future({ Sys.sleep(sleepFor); n }) %...>%
        { . + input$n } %...>%
        as.character()
    })
  })
}

testServer(adderModule, {
  session$setInputs(n = 10)
  timing <- system.time({
    expect_equal(output$sum, "20")
  })
  expect_gt(timing[[3]], 4)
}, sleepFor = 5, n = 10)