Add tests for self.queueMicrotask()

Follows whatwg/html#2789.

html/webappapis/microtask-queuing/queue-microtask-exceptions.any.js

@@ -0,0 +1,15 @@
+"use strict";
+
+setup({
+  allow_uncaught_exception: true
+});
+
+async_test(t => {
+  const error = new Error("boo");
+  self.addEventListener("error", ev => {
+    assert_equals(ev.error, error);
+    t.done();
+  });
+
+  queueMicrotask(() => { throw error; });
+}, "It rethrows exceptions");

html/webappapis/microtask-queuing/queue-microtask.any.js

@@ -0,0 +1,41 @@
+"use strict";
+
+test(() => {
+  assert_equals(typeof queueMicrotask, "function");
+}, "It exists and is a function");
+
+test(() => {
+  assert_throws(new TypeError(), () => queueMicrotask(), "no argument");
+  assert_throws(new TypeError(), () => queueMicrotask(undefined), "undefined");
+  assert_throws(new TypeError(), () => queueMicrotask(null), "null");
+  assert_throws(new TypeError(), () => queueMicrotask(0), "0");
+  assert_throws(new TypeError(), () => queueMicrotask({ handleEvent() { } }), "an event handler object");
+  assert_throws(new TypeError(), () => queueMicrotask("window.x = 5;"), "a string");
+}, "It throws when given non-functions");
+
+async_test(t => {
+  let called = false;
+  queueMicrotask(() => {
+    called = true;
+    t.done();
+  });
+  assert_false(called);
+}, "It calls the callback asynchronously");
+
+async_test(t => {
+  queueMicrotask(function () {
+    assert_array_equals(arguments, []);
+    t.done();
+  }, "x", "y");
+}, "It does not pass any arguments");
+
+async_test(t => {
+  const happenings = [];
+  Promise.resolve().then(() => happenings.push("a"));
+  queueMicrotask(() => happenings.push("b"));
+  Promise.reject().catch(() => happenings.push("c"));
+  queueMicrotask(() => {
+    assert_array_equals(happenings, ["a", "b", "c"]);
+    t.done();
+  });
+}, "It interleaves with promises as expected");

html/webappapis/microtask-queuing/queue-microtask.window.js

@@ -0,0 +1,45 @@
+"use strict";
+
+// This does not work as you expect because mutation observer compound microtasks are confusing.
+// Basically you can only use it once per test.
+function queueMicrotaskViaMO(cb) {
+  const observer = new MutationObserver(cb);
+  const node = document.createTextNode("");
+  observer.observe(node, { characterData: true });
+  node.data = "foo";
+}
+
+// Need to use promise_test to get sequential ordering; otherwise the global mutation observer
+// compound microtask business screws us over.
+
+promise_test(() => {
+  return new Promise(resolve => {
+    const happenings = [];
+
+    queueMicrotaskViaMO(() => happenings.push("x"));
+    queueMicrotask(() => happenings.push("a"));
+
+    queueMicrotask(() => {
+      assert_array_equals(happenings, ["x", "a"]);
+      resolve();
+    });
+  });
+}, "It interleaves with MutationObservers as expected");
+
+promise_test(() => {
+  return new Promise(resolve => {
+    const happenings = [];
+
+    queueMicrotask(() => happenings.push("a"));
+    Promise.reject().catch(() => happenings.push("x"));
+    queueMicrotaskViaMO(() => happenings.push(1));
+    Promise.resolve().then(() => happenings.push("y"));
+    queueMicrotask(() => happenings.push("b"));
+    queueMicrotask(() => happenings.push("c"));
+
+    queueMicrotask(() => {
+      assert_array_equals(happenings, ["a", "x", 1, "y", "b", "c"]);
+      resolve();
+    });
+  });
+}, "It interleaves with MutationObservers and promises together as expected");