2 files changed, 68 insertions, 0 deletions
diff --git a/testing/web-platform/tests/common/test-setting-immutable-prototype.js b/testing/web-platform/tests/common/test-setting-immutable-prototype.js
new file mode 100644
index 0000000000..de9bdd5919
--- /dev/null
+++ b/testing/web-platform/tests/common/test-setting-immutable-prototype.js
@@ -0,0 +1,67 @@
+self.testSettingImmutablePrototypeToNewValueOnly =
+  (prefix, target, newValue, newValueString, { isSameOriginDomain },
+   targetGlobal = window) => {
+  test(() => {
+    assert_throws_js(TypeError, () => {
+      Object.setPrototypeOf(target, newValue);
+    });
+  }, `${prefix}: setting the prototype to ${newValueString} via Object.setPrototypeOf should throw a TypeError`);
+
+  let dunderProtoError = "SecurityError";
+  let dunderProtoErrorName = "\"SecurityError\" DOMException";
+  if (isSameOriginDomain) {
+    // We're going to end up calling the __proto__ setter, which will
+    // enter the Realm of targetGlobal before throwing.
+    dunderProtoError = targetGlobal.TypeError;
+    dunderProtoErrorName = "TypeError";
+  }
+
+  test(() => {
+    const func = function() {
+      target.__proto__ = newValue;
+    };
+    if (isSameOriginDomain) {
+      assert_throws_js(dunderProtoError, func);
+    } else {
+      assert_throws_dom(dunderProtoError, func);
+    }
+  }, `${prefix}: setting the prototype to ${newValueString} via __proto__ should throw a ${dunderProtoErrorName}`);
+
+  test(() => {
+    assert_false(Reflect.setPrototypeOf(target, newValue));
+  }, `${prefix}: setting the prototype to ${newValueString} via Reflect.setPrototypeOf should return false`);
+};
+
+self.testSettingImmutablePrototype =
+  (prefix, target, originalValue, { isSameOriginDomain }, targetGlobal = window) => {
+  const newValue = {};
+  const newValueString = "an empty object";
+  testSettingImmutablePrototypeToNewValueOnly(prefix, target, newValue, newValueString, { isSameOriginDomain }, targetGlobal);
+
+  const originalValueString = originalValue === null ? "null" : "its original value";
+
+  test(() => {
+    assert_equals(Object.getPrototypeOf(target), originalValue);
+  }, `${prefix}: the prototype must still be ${originalValueString}`);
+
+  test(() => {
+    Object.setPrototypeOf(target, originalValue);
+  }, `${prefix}: setting the prototype to ${originalValueString} via Object.setPrototypeOf should not throw`);
+
+  if (isSameOriginDomain) {
+    test(() => {
+      target.__proto__ = originalValue;
+    }, `${prefix}: setting the prototype to ${originalValueString} via __proto__ should not throw`);
+  } else {
+    test(() => {
+      assert_throws_dom("SecurityError", function() {
+        target.__proto__ = newValue;
+      });
+    }, `${prefix}: setting the prototype to ${originalValueString} via __proto__ should throw a "SecurityError" since ` +
+       `it ends up in CrossOriginGetOwnProperty`);
+  }
+
+  test(() => {
+    assert_true(Reflect.setPrototypeOf(target, originalValue));
+  }, `${prefix}: setting the prototype to ${originalValueString} via Reflect.setPrototypeOf should return true`);
+};
diff --git a/testing/web-platform/tests/common/test-setting-immutable-prototype.js.headers b/testing/web-platform/tests/common/test-setting-immutable-prototype.js.headers
new file mode 100644
index 0000000000..6805c323df
--- /dev/null
+++ b/testing/web-platform/tests/common/test-setting-immutable-prototype.js.headers
@@ -0,0 +1 @@
+Content-Type: text/javascript; charset=utf-8