1 files changed, 76 insertions, 0 deletions
diff --git a/js/xpconnect/tests/unit/test_defineESModuleGetters.js b/js/xpconnect/tests/unit/test_defineESModuleGetters.js
new file mode 100644
index 0000000000..f7f12de1d9
--- /dev/null
+++ b/js/xpconnect/tests/unit/test_defineESModuleGetters.js
@@ -0,0 +1,76 @@
+function assertAccessor(lazy, name) {
+  let desc = Object.getOwnPropertyDescriptor(lazy, name);
+  Assert.equal(typeof desc.get, "function");
+  Assert.equal(desc.get.name, name);
+  Assert.equal(typeof desc.set, "function");
+  Assert.equal(desc.set.name, name);
+  Assert.equal(desc.enumerable, true);
+  Assert.equal(desc.configurable, true);
+}
+
+function assertDataProperty(lazy, name, value) {
+  let desc = Object.getOwnPropertyDescriptor(lazy, name);
+  Assert.equal(desc.value, value);
+  Assert.equal(desc.writable, true);
+  Assert.equal(desc.enumerable, true);
+  Assert.equal(desc.configurable, true);
+}
+
+add_task(function test_getter() {
+  // The property should be defined as getter, and getting it should make it
+  // a data property.
+
+  const lazy = {};
+  ChromeUtils.defineESModuleGetters(lazy, {
+    X: "resource://test/esm_lazy-1.sys.mjs",
+  });
+
+  assertAccessor(lazy, "X");
+
+  Assert.equal(lazy.X, 10);
+  assertDataProperty(lazy, "X", 10);
+});
+
+add_task(function test_setter() {
+  // Setting the value before the first get should result in a data property.
+  const lazy = {};
+  ChromeUtils.defineESModuleGetters(lazy, {
+    X: "resource://test/esm_lazy-1.sys.mjs",
+  });
+
+  assertAccessor(lazy, "X");
+  lazy.X = 20;
+  Assert.equal(lazy.X, 20);
+  assertDataProperty(lazy, "X", 20);
+
+  // The above set shouldn't affect the module's value.
+  const lazy2 = {};
+  ChromeUtils.defineESModuleGetters(lazy2, {
+    X: "resource://test/esm_lazy-1.sys.mjs",
+  });
+
+  Assert.equal(lazy2.X, 10);
+});
+
+add_task(function test_order() {
+  // The change to the exported value should be reflected until it's accessed.
+
+  const lazy = {};
+  ChromeUtils.defineESModuleGetters(lazy, {
+    Y: "resource://test/esm_lazy-2.sys.mjs",
+    AddY: "resource://test/esm_lazy-2.sys.mjs",
+  });
+
+  assertAccessor(lazy, "Y");
+  assertAccessor(lazy, "AddY");
+
+  // The change before getting the value should be reflected.
+  lazy.AddY(2);
+  Assert.equal(lazy.Y, 22);
+  assertDataProperty(lazy, "Y", 22);
+
+  // Change after getting the value shouldn't be reflected.
+  lazy.AddY(2);
+  Assert.equal(lazy.Y, 22);
+  assertDataProperty(lazy, "Y", 22);
+});