1 files changed, 68 insertions, 0 deletions
diff --git a/devtools/shared/tests/xpcshell/test_defineLazyPrototypeGetter.js b/devtools/shared/tests/xpcshell/test_defineLazyPrototypeGetter.js
new file mode 100644
index 0000000000..2f53b377de
--- /dev/null
+++ b/devtools/shared/tests/xpcshell/test_defineLazyPrototypeGetter.js
@@ -0,0 +1,68 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test DevToolsUtils.defineLazyPrototypeGetter
+
+function Class() {}
+DevToolsUtils.defineLazyPrototypeGetter(Class.prototype, "foo", () => []);
+
+function run_test() {
+  test_prototype_attributes();
+  test_instance_attributes();
+  test_multiple_instances();
+  test_callback_receiver();
+}
+
+function test_prototype_attributes() {
+  // Check that the prototype has a getter property with expected attributes.
+  const descriptor = Object.getOwnPropertyDescriptor(Class.prototype, "foo");
+  Assert.equal(typeof descriptor.get, "function");
+  Assert.equal(descriptor.set, undefined);
+  Assert.equal(descriptor.enumerable, false);
+  Assert.equal(descriptor.configurable, true);
+}
+
+function test_instance_attributes() {
+  // Instances should not have an own property until the lazy getter has been
+  // activated.
+  const instance = new Class();
+  Assert.ok(!instance.hasOwnProperty("foo"));
+  instance.foo;
+  Assert.ok(instance.hasOwnProperty("foo"));
+
+  // Check that the instance has an own property with the expecred value and
+  // attributes after the lazy getter is activated.
+  const descriptor = Object.getOwnPropertyDescriptor(instance, "foo");
+  Assert.ok(descriptor.value instanceof Array);
+  Assert.equal(descriptor.writable, true);
+  Assert.equal(descriptor.enumerable, false);
+  Assert.equal(descriptor.configurable, true);
+}
+
+function test_multiple_instances() {
+  const instance1 = new Class();
+  const instance2 = new Class();
+  const foo1 = instance1.foo;
+  const foo2 = instance2.foo;
+  // Check that the lazy getter returns the expected type of value.
+  Assert.ok(foo1 instanceof Array);
+  Assert.ok(foo2 instanceof Array);
+  // Make sure the lazy getter runs once and only once per instance.
+  Assert.equal(instance1.foo, foo1);
+  Assert.equal(instance2.foo, foo2);
+  // Make sure each instance gets its own unique value.
+  Assert.notEqual(foo1, foo2);
+}
+
+function test_callback_receiver() {
+  function Foo() {}
+  DevToolsUtils.defineLazyPrototypeGetter(Foo.prototype, "foo", function () {
+    return this;
+  });
+
+  // Check that the |this| value in the callback is the instance itself.
+  const instance = new Foo();
+  Assert.equal(instance.foo, instance);
+}