add __len__ to FutureCollection

CHANGELOG.md

 # v2.18.11
 
 * unit tests migrated to CircleCI
+* added __len__ to FutureCollection

satella/coding/concurrent/futures/collection.py

@@ -22,6 +22,9 @@ class FutureCollection:
             futures = list(futures)
         self.futures = futures
 
+    def __len__(self) -> int:
+        return len(self.futures)
+
     def __getitem__(self, n: int) -> Future:
         return self.futures[n]
 

tests/test_coding/test_concurrent.py

@@ -50,6 +50,8 @@ class TestConcurrent(unittest.TestCase):
         fc += [PythonFuture(), PythonFuture()]
         fc = fc + FutureCollection([PythonFuture()])
         fc + [PythonFuture(), PythonFuture()]
+        fc += FutureCollection([])
+        self.assertGreaterEqual(len(fc), 3)
 
     def test_future_collection_callbacks_one(self):
         a = {'count': 0}