import FIREFOX_52_6_0esr_RELEASE from mozilla-esr52 hg repo

dom/workers/test/test_workersDisabled.html

@@ -0,0 +1,54 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+  <head>
+    <script type="text/javascript" src="/tests/SimpleTest/SimpleTest.js">
+    </script>
+    <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  </head>
+  <body>
+    <script type="text/javascript">
+      SimpleTest.waitForExplicitFinish();
+
+      const enabledPref = "dom.workers.enabled";
+
+      is(SpecialPowers.getBoolPref(enabledPref), true,
+         "Workers should be enabled.");
+
+      SpecialPowers.pushPrefEnv({"set": [[enabledPref, false]]}, test1);
+
+      function test1() {
+        ok(!("Worker" in window), "Worker constructor should not be available.");
+
+        var exception;
+        try {
+          var worker = new Worker("workersDisabled_worker.js");
+        }
+        catch(e) {
+          exception = e;
+        }
+
+        ok(exception, "Shouldn't be able to make a worker.");
+
+        SpecialPowers.pushPrefEnv({"set": [[enabledPref, true]]}, test2);
+      }
+
+      function test2() {
+        ok(("Worker" in window), "Worker constructor should be available.");
+
+        const message = "Hi";
+
+        var worker = new Worker("workersDisabled_worker.js");
+        worker.onmessage = function(event) {
+          is(event.data, message, "Good message.");
+          SimpleTest.finish();
+        }
+        worker.postMessage(message);
+      }
+    </script>
+  </body>
+</html>
+