A shinytest script in testthat

The shiny app

Here is a simple shiny app:

library(shiny)
library(ggplot2)

# UI ####
ui <- fluidPage(
  
  titlePanel("Set axis breaks"),
  
  sidebarLayout(
    # sidebar ####
    sidebarPanel(
      fluidRow(
        column(
          width = 4,
          numericInput("from", "From:", value = NULL)
        ),
        column(
          width = 4,
          numericInput("to", "To:", value = NULL)
        ),
        column(
          width = 4,
          numericInput("by", "By:", value = NULL)
        )
      )
    ),
    
    # main panel ####
    mainPanel(
      plotOutput("ggplot")
    )
  )
)

# SERVER ####
server <- function(input, output) {
  
  FromToBy <- reactiveVal()
  
  observe({
    breaks <- tryCatch({
      seq(input[["from"]], input[["to"]], input[["by"]])
    }, error = function(e) NULL)
    FromToBy(breaks)
  })
  
  scatterplot <- reactive({
    gg <- ggplot(iris, aes(Sepal.Length, Petal.Length)) + geom_point()
    if(!is.null(FromToBy())){
      gg <- gg + scale_y_continuous(breaks = FromToBy())
    }
    gg + theme(
      axis.text = element_text(size = 20),
      axis.title = element_text(size = 18)
    )
  })
  
  output[["ggplot"]] <- renderPlot({
    scatterplot()
  })
  
  observe({ # this is for shinytest - see later ####
    req(scatterplot())
    ggg <- ggplot_build(scatterplot())
    exportTestValues(panelParams = ggg$layout$panel_params[[1L]])
  })
  
}

# Run the application ####
shinyApp(ui = ui, server = server)

It allows to set the breaks of the y-axis of the graph:

Unit test

Say we want to test whether the app correctly sets the axis breaks.

When you have a ggplot, you can get the y-axis breaks as follows:

library(ggplot2)
gg <- ggplot(iris, aes(Sepal.Length, Petal.Length)) + geom_point()
ggg <- ggplot_build(gg)
ggg$layout$panel_params[[1L]][["y.major_source"]]
## [1] 2 4 6

With this piece of code of the app:

observe({ # this is for shinytest - see later ####
  req(scatterplot())
  ggg <- ggplot_build(scatterplot())
  exportTestValues(panelParams = ggg$layout$panel_params[[1L]])
})

we export ggg$layout$panel_params[[1L]].

Assume our package is named shinyFromToBy and the shiny app is saved in file app.R in the inst/shinyApp folder. Then, here is our unit test (to put in the tests/testthat folder):

context("y-axis breaks")

test_that("y-breaks are correct", {

  skip_if_not_installed("shinytest")
  library(shinytest)

  app <- ShinyDriver$new(
    system.file("shinyApp", package = "shinyFromToBy"),
    loadTimeout = 1e+05,
    shinyOptions = list(test.mode = TRUE)
  )
  app$setInputs(from = 1)
  app$setInputs(to = 7)
  app$setInputs(by = 0.5)
  panelParams <- app$getAllValues()$export[["panelParams"]]

  expect_identical(
    panelParams[["y.major_source"]],
    seq(1, 7, by = 0.5)
  )

  app$stop()

})