refactor: replace sendCustomMessage with renderUI in test app, use input_switch

Replace the custom setEnabled JS message handler with renderUI()-based
toggling, which exercises the actual Shiny rendering/re-binding code
path including renderValue re-firing on element replacement. Replace
actionButton toggles with bslib::input_switch for clearer intent.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/testthat/apps/download-button/app.R

@@ -1,7 +1,7 @@
 library(shiny)
 
 # This app covers the three `enabled` values for both downloadButton and downloadLink,
-# plus a simulated shinyjs-disabled case, with toggle buttons for each scenario.
+# plus a simulated shinyjs-disabled case, with toggle switches for each scenario.
 
 # Create a downloadHandler that just serves a simple text file for testing.
 handler <- function() {
@@ -11,69 +11,36 @@ handler <- function() {
   )
 }
 
-# Mirrors what shinyjs::enable() / shinyjs::disable() does: adds/removes the
-# shinyjs-disabled class and the standard disabled attributes. This lets us test
-# that the download buttons/links respond to external JS changes to their enabled state,
-# without making us require shinyjs.
-set_enabled_js <- HTML(
-  "
-  Shiny.addCustomMessageHandler('setEnabled', function(data) {
-    var el = document.getElementById(data.id);
-    if (data.enabled) {
-      el.classList.remove('disabled');
-      el.classList.remove('shinyjs-disabled');
-      el.removeAttribute('aria-disabled');
-      el.removeAttribute('tabindex');
-    } else {
-      el.classList.add('disabled');
-      el.classList.add('shinyjs-disabled');
-      el.setAttribute('aria-disabled', 'true');
-      el.setAttribute('tabindex', '-1');
-    }
-  });
-"
-)
-
 ui <- fluidPage(
-  tags$script(set_enabled_js),
-  # Block of download Button tests
-
   h3("downloadButton"),
 
-  downloadButton("btn_auto", "Auto (default)"),
-  actionButton("toggle_btn_auto", "Toggle"),
+  uiOutput("btn_auto_ui"),
+  bslib::input_switch("toggle_btn_auto", "Enabled", value = TRUE),
 
-  downloadButton("btn_off", "Disabled", enabled = FALSE),
-  actionButton("toggle_btn_off", "Toggle"),
+  uiOutput("btn_off_ui"),
+  bslib::input_switch("toggle_btn_off", "Enabled", value = FALSE),
 
-  downloadButton("btn_on", "Pre-enabled", enabled = TRUE),
-  actionButton("toggle_btn_on", "Toggle"),
+  uiOutput("btn_on_ui"),
+  bslib::input_switch("toggle_btn_on", "Enabled", value = TRUE),
 
   # This mimics what happens when a download button is wrapped in a
   # shinyjs::disabled() call within the UI (and therefore at render time).
-  htmltools::tagAppendAttributes(
-    downloadButton("btn_shinyjs", "shinyjs-disabled"),
-    class = "shinyjs-disabled"
-  ),
-  actionButton("toggle_btn_shinyjs", "Toggle"),
+  uiOutput("btn_shinyjs_ui"),
+  bslib::input_switch("toggle_btn_shinyjs", "Enabled", value = FALSE),
 
-  # Block of download Link tests
   h3("downloadLink"),
 
-  downloadLink("lnk_auto", "Auto (default)"),
-  actionButton("toggle_lnk_auto", "Toggle"),
+  uiOutput("lnk_auto_ui"),
+  bslib::input_switch("toggle_lnk_auto", "Enabled", value = TRUE),
 
-  downloadLink("lnk_off", "Disabled", enabled = FALSE),
-  actionButton("toggle_lnk_off", "Toggle"),
+  uiOutput("lnk_off_ui"),
+  bslib::input_switch("toggle_lnk_off", "Enabled", value = FALSE),
 
-  downloadLink("lnk_on", "Pre-enabled", enabled = TRUE),
-  actionButton("toggle_lnk_on", "Toggle"),
+  uiOutput("lnk_on_ui"),
+  bslib::input_switch("toggle_lnk_on", "Enabled", value = TRUE),
 
-  htmltools::tagAppendAttributes(
-    downloadLink("lnk_shinyjs", "shinyjs-disabled"),
-    class = "shinyjs-disabled"
-  ),
-  actionButton("toggle_lnk_shinyjs", "Toggle")
+  uiOutput("lnk_shinyjs_ui"),
+  bslib::input_switch("toggle_lnk_shinyjs", "Enabled", value = FALSE)
 )
 
 server <- function(input, output, session) {
@@ -86,30 +53,71 @@ server <- function(input, output, session) {
   output$lnk_on <- handler()
   output$lnk_shinyjs <- handler()
 
-  # Each reactiveVal tracks the current intended state, starting from
-  # the post-render-value state (auto/on start enabled; off/shinyjs start disabled).
-  make_toggle <- function(id, initial_enabled) {
-    enabled <- reactiveVal(initial_enabled)
-    observeEvent(input[[paste0("toggle_", id)]], {
-      new_state <- !enabled()
-      enabled(new_state)
-      # This mimics what shinyjs::enable()/disable() would do, which is to send
-      # a message to the client to update the button's enabled state via JS.
-      session$sendCustomMessage(
-        "setEnabled",
-        list(id = id, enabled = new_state)
-      )
-    })
-  }
+  output$btn_auto_ui <- renderUI({
+    if (isTRUE(input$toggle_btn_auto)) {
+      downloadButton("btn_auto", "Auto (default)")
+    } else {
+      downloadButton("btn_auto", "Auto (default)", enabled = FALSE)
+    }
+  })
 
-  make_toggle("btn_auto", TRUE)
-  make_toggle("btn_off", FALSE)
-  make_toggle("btn_on", TRUE)
-  make_toggle("btn_shinyjs", FALSE)
-  make_toggle("lnk_auto", TRUE)
-  make_toggle("lnk_off", FALSE)
-  make_toggle("lnk_on", TRUE)
-  make_toggle("lnk_shinyjs", FALSE)
+  output$btn_off_ui <- renderUI({
+    if (isTRUE(input$toggle_btn_off)) {
+      downloadButton("btn_off", "Disabled", enabled = TRUE)
+    } else {
+      downloadButton("btn_off", "Disabled", enabled = FALSE)
+    }
+  })
+
+  output$btn_on_ui <- renderUI({
+    if (isTRUE(input$toggle_btn_on)) {
+      downloadButton("btn_on", "Pre-enabled", enabled = TRUE)
+    } else {
+      downloadButton("btn_on", "Pre-enabled", enabled = FALSE)
+    }
+  })
+
+  output$btn_shinyjs_ui <- renderUI({
+    btn <- downloadButton("btn_shinyjs", "shinyjs-disabled")
+    if (!isTRUE(input$toggle_btn_shinyjs)) {
+      htmltools::tagAppendAttributes(btn, class = "shinyjs-disabled")
+    } else {
+      btn
+    }
+  })
+
+  output$lnk_auto_ui <- renderUI({
+    if (isTRUE(input$toggle_lnk_auto)) {
+      downloadLink("lnk_auto", "Auto (default)")
+    } else {
+      downloadLink("lnk_auto", "Auto (default)", enabled = FALSE)
+    }
+  })
+
+  output$lnk_off_ui <- renderUI({
+    if (isTRUE(input$toggle_lnk_off)) {
+      downloadLink("lnk_off", "Disabled", enabled = TRUE)
+    } else {
+      downloadLink("lnk_off", "Disabled", enabled = FALSE)
+    }
+  })
+
+  output$lnk_on_ui <- renderUI({
+    if (isTRUE(input$toggle_lnk_on)) {
+      downloadLink("lnk_on", "Pre-enabled", enabled = TRUE)
+    } else {
+      downloadLink("lnk_on", "Pre-enabled", enabled = FALSE)
+    }
+  })
+
+  output$lnk_shinyjs_ui <- renderUI({
+    lnk <- downloadLink("lnk_shinyjs", "shinyjs-disabled")
+    if (!isTRUE(input$toggle_lnk_shinyjs)) {
+      htmltools::tagAppendAttributes(lnk, class = "shinyjs-disabled")
+    } else {
+      lnk
+    }
+  })
 }
 
 shinyApp(ui, server)

tests/testthat/test-downloadButton-shinytest2.R

@@ -17,7 +17,8 @@ app_process <- callr::r_bg(
       port = port,
       host = "127.0.0.1",
       launch.browser = FALSE,
-      quiet = TRUE
+      quiet = TRUE,
+      test.mode = TRUE
     )
   },
   args = list(
@@ -62,7 +63,9 @@ is_disabled <- function(id) {
 # ---------------------------------------------------------------------------
 
 click_toggle <- function(id) {
-  app$click(input = paste0("toggle_", id), wait_ = FALSE)
+  input_name <- paste0("toggle_", id)
+  current <- isTRUE(app$get_value(input = input_name))
+  do.call(app$set_inputs, setNames(list(!current), input_name))
   app$wait_for_idle()
 }