Bug 1305444 - Add test for dispatched method throwing an error; r=Yoric

We didn't have explicit test coverage of this before, surprisingly.

MozReview-Commit-ID: 32ZnxZYLXDg

--HG--
extra : rebase_source : 07110ed90b69c5b0fb73fda8264db2eb755ca6a4

toolkit/components/promiseworker/tests/xpcshell/data/worker.js

@@ -26,5 +26,9 @@ self.addEventListener("message", msg => worker.handleMessage(msg));
 var Agent = {
   bounce: function(...args) {
     return args;
-  }
+  },
+
+  throwError: function(msg, ...args) {
+     throw new Error(msg);
+  },
 };

toolkit/components/promiseworker/tests/xpcshell/test_Promise.js

@@ -106,3 +106,12 @@ add_task(function* test_transfer_with_meta() {
     Assert.equal(result[i], i);
   }
 });
+
+add_task(function* test_throw_error() {
+  try {
+    yield worker.post("throwError", ["error message"]);
+    Assert.ok(false, "should have thrown");
+  } catch (ex) {
+    Assert.equal(ex.message, "Error: error message");
+  }
+});