test(Subscription): add test for adding errant custom subscription to…

… unsubscribed subscription

- tries to synchronously add a custom subscription that throws when unsubscribed to a Subscription that is mid-unsubscribe and therefor
  flagged `isUnsubscribed`. It's an edge-case, but it should work.

fixes #1256

spec/Subscription-spec.js

@@ -31,7 +31,47 @@ describe('Subscription', function () {
     setTimeout(function () {
       expect(function () {
         subscription.unsubscribe();
-      }).toThrow();
+      }).toThrow(new Rx.UnsubscriptionError([new Error('oops, I am a bad unsubscribe!')]));
+      expect(tearDowns).toEqual([1, 2, 3]);
+      done();
+    });
+  });
+
+  it('should not leak when adding a bad custom subscription to a subscription', function (done) {
+    var tearDowns = [];
+
+    var sub = new Subscription();
+
+    var source1 = Observable.create(function (observer) {
+      return function () {
+        tearDowns.push(1);
+      };
+    });
+
+    var source2 = Observable.create(function (observer) {
+      return function () {
+        tearDowns.push(2);
+        sub.add({
+          unsubscribe: function () {
+            expect(sub.isUnsubscribed).toBe(true);
+            throw new Error('Who is your daddy, and what does he do?');
+          }
+        });
+      };
+    });
+
+    var source3 = Observable.create(function (observer) {
+      return function () {
+        tearDowns.push(3);
+      };
+    });
+
+    sub.add(Observable.merge(source1, source2, source3).subscribe());
+
+    setTimeout(function () {
+      expect(function () {
+        sub.unsubscribe();
+      }).toThrow(new Rx.UnsubscriptionError([new Error('Who is your daddy, and what does he do?')]));
       expect(tearDowns).toEqual([1, 2, 3]);
       done();
     });