1 files changed, 69 insertions, 0 deletions
diff --git a/modules/libpref/test/unit/test_warnings.js b/modules/libpref/test/unit/test_warnings.js
new file mode 100644
index 000000000..856e117b7
--- /dev/null
+++ b/modules/libpref/test/unit/test_warnings.js
@@ -0,0 +1,69 @@
+/* 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 http://mozilla.org/MPL/2.0/. */
+
+Cu.import("resource://gre/modules/Promise.jsm");
+
+var cs = Cc["@mozilla.org/consoleservice;1"].
+  getService(Ci.nsIConsoleService);
+var ps = Cc["@mozilla.org/preferences-service;1"].
+  getService(Ci.nsIPrefService);
+
+function makeBuffer(length) {
+  return new Array(length + 1).join('x');
+}
+
+/**
+ * @resolves |true| if execution proceeded without warning,
+ * |false| if there was a warning.
+ */
+function checkWarning(pref, buffer) {
+  let deferred = Promise.defer();
+  let complete = false;
+  let listener = {
+    observe: function(event) {
+      let message = event.message;
+      if (!(message.startsWith("Warning: attempting to write")
+            && message.includes(pref))) {
+        return;
+      }
+      if (complete) {
+        return;
+      }
+      complete = true;
+      do_print("Warning while setting " + pref);
+      cs.unregisterListener(listener);
+      deferred.resolve(true);
+    }
+  };
+  do_timeout(1000, function() {
+    if (complete) {
+      return;
+    }
+    complete = true;
+    do_print("No warning while setting " + pref);
+    cs.unregisterListener(listener);
+    deferred.resolve(false);
+  });
+  cs.registerListener(listener);
+  ps.setCharPref(pref, buffer);
+  return deferred.promise;
+}
+
+function run_test() {
+  run_next_test();
+}
+
+add_task(function() {
+  // Simple change, shouldn't cause a warning
+  do_print("Checking that a simple change doesn't cause a warning");
+  let buf = makeBuffer(100);
+  let warned = yield checkWarning("string.accept", buf);
+  do_check_false(warned);
+
+  // Large change, should cause a warning
+  do_print("Checking that a large change causes a warning");
+  buf = makeBuffer(32 * 1024);
+  warned = yield checkWarning("string.warn", buf);
+  do_check_true(warned);
+});