1 files changed, 51 insertions, 0 deletions
diff --git a/devtools/client/inspector/markup/test/browser_markup_shadowdom_show_nodes_button.js b/devtools/client/inspector/markup/test/browser_markup_shadowdom_show_nodes_button.js
new file mode 100644
index 0000000000..54685bc470
--- /dev/null
+++ b/devtools/client/inspector/markup/test/browser_markup_shadowdom_show_nodes_button.js
@@ -0,0 +1,51 @@
+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test that the "Show all 'N' nodes" button displays the proper value
+
+const NODE_COUNT = 101;
+const TEST_URL = `data:text/html;charset=utf-8,
+  <test-component>
+  </test-component>
+
+  <script>
+    'use strict';
+    for (let i = 0; i < ${NODE_COUNT}; i++) {
+      const div = document.createElement("div");
+      div.innerHTML = i;
+      document.querySelector('test-component').appendChild(div);
+    }
+    customElements.define('test-component', class extends HTMLElement {
+      constructor() {
+        super();
+        let shadowRoot = this.attachShadow({mode: 'open'});
+        shadowRoot.innerHTML = '<slot></slot>';
+      }
+    });
+  </script>`;
+
+add_task(async function () {
+  const { inspector } = await openInspectorForURL(TEST_URL);
+  const { markup } = inspector;
+
+  info("Find and expand the component shadow DOM host.");
+  const hostFront = await getNodeFront("test-component", inspector);
+  const hostContainer = markup.getContainer(hostFront);
+  await expandContainer(inspector, hostContainer);
+  const shadowRootContainer = hostContainer.getChildContainers()[0];
+  await expandContainer(inspector, shadowRootContainer);
+
+  info("Expand the slot");
+  const slotContainer = shadowRootContainer.getChildContainers()[0];
+  await expandContainer(inspector, slotContainer);
+
+  info("Find the 'Show all nodes' button");
+  const button = slotContainer.elt.querySelector("button");
+  console.log(button);
+  ok(
+    button.innerText.includes(NODE_COUNT),
+    "'Show all nodes' button contains correct node count"
+  );
+});