1 files changed, 40 insertions, 0 deletions
diff --git a/devtools/server/tests/xpcshell/test_objectgrips-sparse-array.js b/devtools/server/tests/xpcshell/test_objectgrips-sparse-array.js
new file mode 100644
index 0000000000..76a6b32f4b
--- /dev/null
+++ b/devtools/server/tests/xpcshell/test_objectgrips-sparse-array.js
@@ -0,0 +1,40 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+Services.prefs.setBoolPref("security.allow_eval_with_system_principal", true);
+registerCleanupFunction(() => {
+  Services.prefs.clearUserPref("security.allow_eval_with_system_principal");
+});
+
+add_task(
+  threadFrontTest(async ({ threadFront, debuggee }) => {
+    const packet = await executeOnNextTickAndWaitForPause(
+      () => evalCode(debuggee),
+      threadFront
+    );
+
+    const [grip] = packet.frame.arguments;
+    await threadFront.resume();
+
+    strictEqual(grip.class, "Array", "The grip has an Array class");
+
+    const { items } = grip.preview;
+    strictEqual(items[0], null, "The empty slot has null as grip preview");
+    deepEqual(
+      items[1],
+      { type: "undefined" },
+      "The undefined value has grip value of type undefined"
+    );
+  })
+);
+
+function evalCode(debuggee) {
+  debuggee.eval(
+    function stopMe(arr) {
+      debugger;
+    }.toString()
+  );
+  debuggee.eval("stopMe([, undefined])");
+}