diff --git a/inst/apps/312-bslib-sidebar-resize/app.R b/inst/apps/312-bslib-sidebar-resize/app.R
index 2c374d4d57..23328c1bb1 100644
--- a/inst/apps/312-bslib-sidebar-resize/app.R
+++ b/inst/apps/312-bslib-sidebar-resize/app.R
@@ -18,9 +18,12 @@ lorem2 <- p(
 
 ui <- page_navbar(
   title = "312 | bslib-sidebar-resize",
-  theme = bs_theme("bslib-sidebar-transition-duration" = "3s"),
+  theme = bs_theme(
+    "bslib-sidebar-transition-duration" = Sys.getenv("SIDEBAR_TRANSITION_TIME", "0.5s")
+  ),
   sidebar = sidebar(
     title = "Shared Sidebar",
+    id = "sidebar-shared",
     open = "open",
     p("The plots should resize smoothly when this sidebar or the local sidebar are toggled.")
   ),
@@ -33,9 +36,13 @@ ui <- page_navbar(
       "update the plot with the final dimensions."
     ),
     layout_sidebar(
-      sidebar = sidebar(title = "Toggle me", lorem1, lorem2, lorem1),
+      sidebar = sidebar(
+        title = "Toggle me",
+        id = "sidebar-local-static",
+        lorem1, lorem2, lorem1
+      ),
       lorem1,
-      plotOutput("plot_static1"),
+      plotOutput("plot_static_local"),
       lorem2
     ),
     h2("Shared only", class = "my-3"),
@@ -44,8 +51,8 @@ ui <- page_navbar(
     ),
     div(
       class = "row",
-      div(class = "col", plotOutput("plot_static2")),
-      div(class = "col", p(lorem2, lorem1))
+      div(class = "col-6", plotOutput("plot_static_shared")),
+      div(class = "col-6", lorem2, lorem1)
     )
   ),
   nav(
@@ -57,9 +64,13 @@ ui <- page_navbar(
       "complete."
     ),
     layout_sidebar(
-      sidebar = sidebar(title = "Toggle me", lorem1, lorem2, lorem1),
+      sidebar = sidebar(
+        title = "Toggle me",
+        id = "sidebar-local-widget",
+        lorem1, lorem2, lorem1
+      ),
       lorem1,
-      plotlyOutput("plot_widget1"),
+      plotlyOutput("plot_widget_local"),
       lorem2
     ),
     h2("Shared only", class = "my-3"),
@@ -68,8 +79,8 @@ ui <- page_navbar(
     ),
     div(
       class = "row",
-      div(class = "col", plotlyOutput("plot_widget2")),
-      div(class = "col", p(lorem2, lorem1))
+      div(class = "col-6", plotlyOutput("plot_widget_shared")),
+      div(class = "col-6", lorem2, lorem1)
     )
   ),
   footer = div(style = "min-height: 100vh")
@@ -88,11 +99,11 @@ server <- function(input, output, session) {
       theme_gray(base_size = 16)
   })
 
-  output$plot_static1 <- renderPlot(plot())
-  output$plot_static2 <- renderPlot(plot())
+  output$plot_static_local <- renderPlot(plot())
+  output$plot_static_shared <- renderPlot(plot())
 
-  output$plot_widget1 <- renderPlotly(ggplotly(plot()))
-  output$plot_widget2 <- renderPlotly(ggplotly(plot()))
+  output$plot_widget_local <- renderPlotly(ggplotly(plot()))
+  output$plot_widget_shared <- renderPlotly(ggplotly(plot()))
 }
 
 shinyApp(ui, server)
diff --git a/inst/apps/312-bslib-sidebar-resize/tests/testthat.R b/inst/apps/312-bslib-sidebar-resize/tests/testthat.R
new file mode 100644
index 0000000000..7d25b5b9e4
--- /dev/null
+++ b/inst/apps/312-bslib-sidebar-resize/tests/testthat.R
@@ -0,0 +1 @@
+shinytest2::test_app()
diff --git a/inst/apps/312-bslib-sidebar-resize/tests/testthat/setup-shinytest2.R b/inst/apps/312-bslib-sidebar-resize/tests/testthat/setup-shinytest2.R
new file mode 100644
index 0000000000..be65b4f035
--- /dev/null
+++ b/inst/apps/312-bslib-sidebar-resize/tests/testthat/setup-shinytest2.R
@@ -0,0 +1,2 @@
+# Load application support files into testing environment
+shinytest2::load_app_env()
diff --git a/inst/apps/312-bslib-sidebar-resize/tests/testthat/test-shinytest2.R b/inst/apps/312-bslib-sidebar-resize/tests/testthat/test-shinytest2.R
new file mode 100644
index 0000000000..b301e87bb4
--- /dev/null
+++ b/inst/apps/312-bslib-sidebar-resize/tests/testthat/test-shinytest2.R
@@ -0,0 +1,257 @@
+library(shinytest2)
+
+expect_sidebar_hidden_factory <- function(app) {
+  function(id) {
+    state <- app$get_js(js_sidebar_state(id = id))
+    expect_true("sidebar-collapsed" %in% state$layout_classes)
+    expect_equal(state$content_display, "none")
+    expect_true(state$sidebar_hidden)
+  }
+}
+
+expect_sidebar_shown_factory <- function(app) {
+  function(id) {
+    state <- app$get_js(js_sidebar_state(id = id))
+    expect_false("sidebar-collapsed" %in% state$layout_classes)
+    expect_false(identical(state$content_display, "none"))
+    expect_false(state$sidebar_hidden)
+  }
+}
+
+js_sidebar_transition_complete <- function(id) {
+  sprintf(
+    "!document.getElementById('%s').parentElement.classList.contains('transitioning');",
+    id
+  )
+}
+
+js_sidebar_state <- function(id) {
+  sprintf(
+    "(function() {
+      return {
+      layout_classes: Array.from(document.getElementById('%s').closest('.bslib-sidebar-layout').classList),
+      content_display: window.getComputedStyle(document.querySelector('#%s .sidebar-content')).getPropertyValue('display'),
+      sidebar_hidden: document.getElementById('%s').hidden
+    }})();",
+    id, id, id
+  )
+}
+
+js_element_width <- function(selector) {
+  sprintf(
+    "document.querySelector('%s').getBoundingClientRect().width;",
+    selector
+  )
+}
+
+# Gather width measurements of plots during the sidebar transition
+#
+# 1. Measures the `initial` width of plots prior to transition
+# 2. Clicks the sidebar toggle
+# 3. Samples width of plots `during` transition
+# 4. Waits for transition to complete
+# 5. Measures the `final` width of plots after transition
+# 6. Captures updated shiny `outputs` during the measurement period
+watch_sidebar_transition <- function(
+  app,
+  sidebar = c("shared", "local"),
+  page = c("static", "widget")
+) {
+  sidebar <- match.arg(sidebar)
+  page <- match.arg(page)
+
+  id_sidebar <- if (sidebar == "shared") "sidebar-shared" else paste0("sidebar-local-", page)
+  sel_plot <- function(which = c("shared", "local")) {
+    plot_container <-
+      if (page == "static") {
+        "img"
+      } else {
+        ".plot-container > .svg-container"
+      }
+    paste0("#plot_", page, "_", which, " > ", plot_container)
+  }
+  sel_plot_img_local <- sel_plot("local")
+  sel_plot_img_shared <- sel_plot("shared")
+
+  initial <- list(
+    local = app$get_js(js_element_width(sel_plot_img_local)),
+    shared = app$get_js(js_element_width(sel_plot_img_shared))
+  )
+
+  during <- list(local = c(), shared = c())
+
+  app$run_js("
+if (!window.updatedOutputs) {
+  $(document).on('shiny:value', function(event) {
+    window.updatedOutputs.push(event.target.id);
+  })
+}
+window.updatedOutputs = [];
+")
+  app$click(selector = sprintf("#%s + .collapse-toggle", id_sidebar))
+
+  while (!app$get_js(js_sidebar_transition_complete(id_sidebar))) {
+    Sys.sleep(0.1)
+    during$local <- c(during$local, app$get_js(js_element_width(sel_plot_img_local)))
+    during$shared <- c(during$shared, app$get_js(js_element_width(sel_plot_img_shared)))
+  }
+
+  if (page == "static") {
+    app$wait_for_js("window.updatedOutputs.length > 0")
+    Sys.sleep(0.25)
+  } else {
+    # widget plots don't trigger shiny:value events, so we just have to wait
+    Sys.sleep(1)
+  }
+
+  outputs <- app$get_js("window.updatedOutputs")
+  final <- list(
+    local = app$get_js(js_element_width(sel_plot_img_local)),
+    shared = app$get_js(js_element_width(sel_plot_img_shared))
+  )
+
+  list(
+    initial = initial,
+    during = during,
+    final = final,
+    outputs = unlist(outputs)
+  )
+}
+
+# 312-bslib-sidebar-resize ----------------------------------------------------
+test_that("312-bslib-sidebar-resize", {
+  app <- AppDriver$new(
+    name = "312-bslib-sidebar-resize",
+    variant = platform_variant(),
+    height = 1600,
+    width = 1200,
+    view = interactive(),
+    options = list(bslib.precompiled = FALSE),
+    expect_values_screenshot_args = FALSE
+  )
+
+  expect_sidebar_hidden <- expect_sidebar_hidden_factory(app)
+  expect_sidebar_shown <- expect_sidebar_shown_factory(app)
+
+  # STATIC PAGE ================================================================
+
+  # collapse static shared sidebar --------
+  close_static_shared <- watch_sidebar_transition(
+    app,
+    sidebar = "shared",
+    page = "static"
+  )
+
+  expect_sidebar_hidden("sidebar-shared")
+
+  # plot output image size changed during collapse for both plots
+  expect_gt(length(unique(close_static_shared$during$local)), 1)
+  expect_gt(length(unique(close_static_shared$during$shared)), 1)
+
+  # plot output image size was growing during transition
+  expect_gt(min(close_static_shared$during$local), close_static_shared$initial$local)
+  expect_gt(min(close_static_shared$during$shared), close_static_shared$initial$shared)
+
+  # both plots updated at the end of the transition
+  expect_setequal(close_static_shared$outputs, c("plot_static_local", "plot_static_shared"))
+
+  # collapse static local sidebar --------
+  close_static_local <- watch_sidebar_transition(
+    app,
+    sidebar = "local",
+    page = "static"
+  )
+
+  expect_sidebar_hidden("sidebar-local-static")
+
+  # plot output image size changed during collapse for local plot only
+  expect_gt(length(unique(close_static_local$during$local)), 1)
+  expect_equal(length(unique(close_static_local$during$shared)), 1)
+
+  # plot output image size was growing during transition for local only
+  expect_gt(min(close_static_local$during$local), close_static_local$initial$local)
+  expect_equal(unique(close_static_local$during$shared), close_static_local$initial$shared)
+
+  # local plot updated at the end of the transition
+  expect_equal(close_static_local$outputs, "plot_static_local")
+
+  # expand static shared sidebar --------
+  open_static_shared <- watch_sidebar_transition(
+    app,
+    sidebar = "shared",
+    page = "static"
+  )
+
+  expect_sidebar_shown("sidebar-shared")
+
+  # plot output image size changed during expand for both plots
+  expect_gt(length(unique(open_static_shared$during$local)), 1)
+  expect_gt(length(unique(open_static_shared$during$shared)), 1)
+
+  # plot output image size was shrinking during transition
+  expect_lt(max(open_static_shared$during$local), open_static_shared$initial$local)
+  expect_lt(max(open_static_shared$during$shared), open_static_shared$initial$shared)
+
+  # both plots updated at the end of the transition
+  expect_setequal(open_static_shared$outputs, c("plot_static_local", "plot_static_shared"))
+
+  # SWITCH TO WIDGET PAGE ======================================================
+  app$
+    click(selector = '.nav-link[data-value="Widget"]')$
+    wait_for_js("document.getElementById('js-plotly-tester') ? true : false")
+
+  # now we repeat all of the same tests above, except that the widget resizing
+  # won't trigger a 'shiny:value' event.
+
+  # collapse widget shared sidebar --------
+  close_widget_shared <- watch_sidebar_transition(
+    app,
+    sidebar = "shared",
+    page = "widget"
+  )
+
+  expect_sidebar_hidden("sidebar-shared")
+
+  # plot output image size changed during collapse for both plots
+  expect_gt(length(unique(close_widget_shared$during$local)), 1)
+  expect_gt(length(unique(close_widget_shared$during$shared)), 1)
+
+  # plot output image size was growing during transition
+  expect_gt(min(close_widget_shared$during$local), close_widget_shared$initial$local)
+  expect_gt(min(close_widget_shared$during$shared), close_widget_shared$initial$shared)
+
+  # collapse widget local sidebar --------
+  close_widget_local <- watch_sidebar_transition(
+    app,
+    sidebar = "local",
+    page = "widget"
+  )
+
+  expect_sidebar_hidden("sidebar-local-widget")
+
+  # plot output image size changed during collapse for local plot only
+  expect_gt(length(unique(close_widget_local$during$local)), 1)
+  expect_equal(length(unique(close_widget_local$during$shared)), 1)
+
+  # plot output image size was growing during transition for local only
+  expect_gt(min(close_widget_local$during$local), close_widget_local$initial$local)
+  expect_equal(unique(close_widget_local$during$shared), close_widget_local$initial$shared)
+
+  # expand widget shared sidebar --------
+  open_widget_shared <- watch_sidebar_transition(
+    app,
+    sidebar = "shared",
+    page = "widget"
+  )
+
+  expect_sidebar_shown("sidebar-shared")
+
+  # plot output image size changed during expand for both plots
+  expect_gt(length(unique(open_widget_shared$during$local)), 1)
+  expect_gt(length(unique(open_widget_shared$during$shared)), 1)
+
+  # plot output image size was shrinking during transition
+  expect_lt(max(open_widget_shared$during$local), open_widget_shared$initial$local)
+  expect_lt(max(open_widget_shared$during$shared), open_widget_shared$initial$shared)
+
+})