Implement TestUtils (#36301)

Implement the TestUtils namespace from
https://testutils.spec.whatwg.org/.
This should make the `js/builtins/weakrefs` tests run faster and more
consistently.

This change will enable other WPT tests but no tests exist currently for
TestUtils itself.
Fixes: #36290

---------

Signed-off-by: Sebastian C <sebsebmc@gmail.com>
Signed-off-by: sagudev <16504129+sagudev@users.noreply.github.com>
Co-authored-by: sagudev <16504129+sagudev@users.noreply.github.com>

1 files changed, 49 insertions, 0 deletions

diff --git a/components/script/dom/testutils.rs b/components/script/dom/testutils.rs
new file mode 100644
index 00000000000..4aadac05da3
--- /dev/null
+++ b/components/script/dom/testutils.rs
@@ -0,0 +1,49 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+use std::rc::Rc;
+
+use dom_struct::dom_struct;
+use js::jsapi::{GCReason, JS_GC};
+use script_bindings::reflector::Reflector;
+use script_bindings::script_runtime::CanGc;
+
+use super::globalscope::GlobalScope;
+use crate::dom::bindings::codegen::Bindings::TestUtilsBinding::TestUtilsMethods;
+use crate::dom::promise::Promise;
+use crate::test::TrustedPromise;
+
+#[dom_struct]
+pub(crate) struct TestUtils {
+    reflector_: Reflector,
+}
+
+impl TestUtilsMethods<crate::DomTypeHolder> for TestUtils {
+    /// <https://testutils.spec.whatwg.org/#dom-testutils-gc>
+    #[allow(unsafe_code)]
+    fn Gc(global: &GlobalScope) -> Rc<Promise> {
+        // 1. Let p be a new promise.
+        let promise = Promise::new(global, CanGc::note());
+        let trusted = TrustedPromise::new(promise.clone());
+        // 2. Run the following in parallel:
+        // 2.1 Run implementation-defined steps to perform a garbage collection covering at least the entry Realm.
+        // 2.2 Resolve p.
+        // We need to spin the event-loop in order get the GC to actually run.
+        // We do this by queuing a task that calls the GC and then resolves the promise.
+        let task = task!(testutils_gc: move || {
+            unsafe {
+                JS_GC(*GlobalScope::get_cx(), GCReason::DOM_TESTUTILS);
+            }
+            let promise = trusted.root();
+            promise.resolve_native(&(), CanGc::note());
+        });
+
+        global
+            .task_manager()
+            .dom_manipulation_task_source()
+            .queue(task);
+
+        promise
+    }
+}