我的应用程序返回一个ggplot -或-一条消息给用户，说明为什么没有生成绘图
使用validate(need())创建消息
我还没有能够弄清楚如何使这与shinytest 2工作
下面是来自Robust testing的示例，已更新以显示我正在尝试做的事情
应用程序文件：

# initial example from
#   https://rstudio.github.io/shinytest2/articles/robust.html
# removed depreciated aes_string()

library(shiny)
library(ggplot2)
ui <- fluidPage(
  numericInput("n", "Number of rows", 10, 1, nrow(cars)),
  plotOutput("plot")
)
server <- function(input, output) {
  dt <- reactive({
    head(cars, input$n)
  })
  plot_obj <- reactive({
    validate(need(input$n > 0, message = "n must be strictly positive"))
    ggplot(dt(), aes(speed, dist)) + geom_point()
  })

  output$plot <- renderPlot({
    plot_obj()
  })

  exportTestValues(
    dt = dt(),
    plot_obj = plot_obj()
  )
}
plot_app <- shinyApp(ui = ui, server = server)
plot_app

测试文件：

# File: tests/testthat/test-export.R
library(shinytest2)

test_that("`export`ed `plot_obj` is updated by `n`", {
  skip_if_not_installed("vdiffr")

  app <- AppDriver$new(variant = platform_variant())

  expect_n_and_plot <- function(n) {
    # Verify `n` input equals `n`
    n_val <- app$get_value(input = "n")
    expect_equal(n_val, n, expected.label = n)
    # Verify `dt()` data is first `n` lines of `cars`
    dt <- app$get_value(export = "dt")
    expect_equal(dt, head(cars, n), expected.label = paste0("head(cars, ", n, ")"))

    # Verify `plot_obj()` data is `dt()`
    plot_obj <- app$get_value(export = "plot_obj")
    expect_equal(plot_obj$data, dt, info = paste0("n = ", n))
    # Verify `plot_obj()` is consistent
    vdiffr::expect_doppelganger(paste0("cars-points-", n), plot_obj)
  }

  expect_n_and_plot(10)

  # Update `n` to 20
  app$set_inputs(n = 20)
  expect_n_and_plot(20)

  # Update `n` to -1, expect message
  app$set_inputs(n = -1)
  expect_n_and_plot(-1)
})

理想情况下，回归测试会像标准输出一样捕获返回的消息
谢谢你考虑这个