googleapis
diff --git a/tests/unit/test_grpc_helpers.py b/tests/unit/test_grpc_helpers.py
@@ -66,6 +66,128 @@ def test_wrap_unary_errors():
     assert exc_info.value.response == grpc_error
 
 
+class Test_StreamingResponseIterator:
+    @staticmethod
+    def _make_wrapped(*items):
+        return iter(items)
+
+    @staticmethod
+    def _make_one(wrapped, **kw):
+        return grpc_helpers._StreamingResponseIterator(wrapped, **kw)
+
+    def test_ctor_defaults(self):
+        wrapped = self._make_wrapped("a", "b", "c")
+        iterator = self._make_one(wrapped)
+        assert iterator._stored_first_result == "a"
+        assert list(wrapped) == ["b", "c"]
+
+    def test_ctor_explicit(self):
+        wrapped = self._make_wrapped("a", "b", "c")
+        iterator = self._make_one(wrapped, prefetch_first_result=False)
+        assert getattr(iterator, "_stored_first_result", self) is self
+        assert list(wrapped) == ["a", "b", "c"]
+
+    def test_ctor_w_rpc_error_on_prefetch(self):
+        wrapped = mock.MagicMock()
+        wrapped.__next__.side_effect = grpc.RpcError()
+
+        with pytest.raises(grpc.RpcError):
+            self._make_one(wrapped)
+
+    def test___iter__(self):
+        wrapped = self._make_wrapped("a", "b", "c")
+        iterator = self._make_one(wrapped)
+        assert iter(iterator) is iterator
+
+    def test___next___w_cached_first_result(self):
+        wrapped = self._make_wrapped("a", "b", "c")
+        iterator = self._make_one(wrapped)
+        assert next(iterator) == "a"
+        iterator = self._make_one(wrapped, prefetch_first_result=False)
+        assert next(iterator) == "b"
+        assert next(iterator) == "c"
+
+    def test___next___wo_cached_first_result(self):
+        wrapped = self._make_wrapped("a", "b", "c")
+        iterator = self._make_one(wrapped, prefetch_first_result=False)
+        assert next(iterator) == "a"
+        assert next(iterator) == "b"
+        assert next(iterator) == "c"
+
+    def test___next___w_rpc_error(self):
+        wrapped = mock.MagicMock()
+        wrapped.__next__.side_effect = grpc.RpcError()
+        iterator = self._make_one(wrapped, prefetch_first_result=False)
+
+        with pytest.raises(exceptions.GoogleAPICallError):
+            next(iterator)
+
+    def test_add_callback(self):
+        wrapped = mock.MagicMock()
+        callback = mock.Mock(spec={})
+        iterator = self._make_one(wrapped, prefetch_first_result=False)
+
+        assert iterator.add_callback(callback) is wrapped.add_callback.return_value
+
+        wrapped.add_callback.assert_called_once_with(callback)
+
+    def test_cancel(self):
+        wrapped = mock.MagicMock()
+        iterator = self._make_one(wrapped, prefetch_first_result=False)
+
+        assert iterator.cancel() is wrapped.cancel.return_value
+
+        wrapped.cancel.assert_called_once_with()
+
+    def test_code(self):
+        wrapped = mock.MagicMock()
+        iterator = self._make_one(wrapped, prefetch_first_result=False)
+
+        assert iterator.code() is wrapped.code.return_value
+
+        wrapped.code.assert_called_once_with()
+
+    def test_details(self):
+        wrapped = mock.MagicMock()
+        iterator = self._make_one(wrapped, prefetch_first_result=False)
+
+        assert iterator.details() is wrapped.details.return_value
+
+        wrapped.details.assert_called_once_with()
+
+    def test_initial_metadata(self):
+        wrapped = mock.MagicMock()
+        iterator = self._make_one(wrapped, prefetch_first_result=False)
+
+        assert iterator.initial_metadata() is wrapped.initial_metadata.return_value
+
+        wrapped.initial_metadata.assert_called_once_with()
+
+    def test_is_active(self):
+        wrapped = mock.MagicMock()
+        iterator = self._make_one(wrapped, prefetch_first_result=False)
+
+        assert iterator.is_active() is wrapped.is_active.return_value
+
+        wrapped.is_active.assert_called_once_with()
+
+    def test_time_remaining(self):
+        wrapped = mock.MagicMock()
+        iterator = self._make_one(wrapped, prefetch_first_result=False)
+
+        assert iterator.time_remaining() is wrapped.time_remaining.return_value
+
+        wrapped.time_remaining.assert_called_once_with()
+
+    def test_trailing_metadata(self):
+        wrapped = mock.MagicMock()
+        iterator = self._make_one(wrapped, prefetch_first_result=False)
+
+        assert iterator.trailing_metadata() is wrapped.trailing_metadata.return_value
+
+        wrapped.trailing_metadata.assert_called_once_with()
+
+
 def test_wrap_stream_okay():
     expected_responses = [1, 2, 3]
     callable_ = mock.Mock(spec=["__call__"], return_value=iter(expected_responses))