1 files changed, 85 insertions, 0 deletions
diff --git a/devtools/shared/commands/script/tests/browser_script_command_execute_last_result.js b/devtools/shared/commands/script/tests/browser_script_command_execute_last_result.js
new file mode 100644
index 0000000000..aebdaeb168
--- /dev/null
+++ b/devtools/shared/commands/script/tests/browser_script_command_execute_last_result.js
@@ -0,0 +1,85 @@
+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Testing that last evaluation result can be accessed with `$_`
+
+add_task(async () => {
+  const tab = await addTab(`data:text/html;charset=utf-8,`);
+
+  const commands = await CommandsFactory.forTab(tab);
+  await commands.targetCommand.startListening();
+
+  info("$_ returns undefined if nothing has evaluated yet");
+  let response = await commands.scriptCommand.execute("$_");
+  basicResultCheck(response, "$_", { type: "undefined" });
+
+  info("$_ returns last value and performs basic arithmetic");
+  response = await commands.scriptCommand.execute("2+2");
+  basicResultCheck(response, "2+2", 4);
+
+  response = await commands.scriptCommand.execute("$_");
+  basicResultCheck(response, "$_", 4);
+
+  response = await commands.scriptCommand.execute("$_ + 2");
+  basicResultCheck(response, "$_ + 2", 6);
+
+  response = await commands.scriptCommand.execute("$_ + 4");
+  basicResultCheck(response, "$_ + 4", 10);
+
+  info("$_ has correct references to objects");
+  response = await commands.scriptCommand.execute("var foo = {bar:1}; foo;");
+  basicResultCheck(response, "var foo = {bar:1}; foo;", {
+    type: "object",
+    class: "Object",
+    actor: /[a-z]/,
+  });
+  checkObject(response.result.getGrip().preview.ownProperties, {
+    bar: {
+      value: 1,
+    },
+  });
+
+  response = await commands.scriptCommand.execute("$_");
+  basicResultCheck(response, "$_", {
+    type: "object",
+    class: "Object",
+    actor: /[a-z]/,
+  });
+  checkObject(response.result.getGrip().preview.ownProperties, {
+    bar: {
+      value: 1,
+    },
+  });
+
+  info(
+    "Update a property value and check that evaluating $_ returns the expected object instance"
+  );
+  await ContentTask.spawn(gBrowser.selectedBrowser, null, () => {
+    content.wrappedJSObject.foo.bar = "updated_value";
+  });
+
+  response = await commands.scriptCommand.execute("$_");
+  basicResultCheck(response, "$_", {
+    type: "object",
+    class: "Object",
+    actor: /[a-z]/,
+  });
+  checkObject(response.result.getGrip().preview.ownProperties, {
+    bar: {
+      value: "updated_value",
+    },
+  });
+
+  await commands.destroy();
+});
+
+function basicResultCheck(response, input, output) {
+  checkObject(response, {
+    input,
+    result: output,
+  });
+  ok(!response.exception, "no eval exception");
+  ok(!response.helperResult, "no helper result");
+}