Mock async iterators properly

By default AsyncMock doesn't provide any proper mocking of async
async iterators, and if we just assign a `AsyncMock` to stub calls like
`ReceivePublicTradesStream`, what happens is that
`async for x in ReceivePublicTradesStream()` is used instead. What
Python does with this is something like:

```py
stream = ReceivePublicTradesStream()
it = stream.__aiter__()  # Gets an anync iterator, but this call is sync
while v := await it.__anext():
    ...
```

Because `ReceivePublicTradesStream` is an `AsyncMock`, getting any
attributes (like `__aiter__()`) results in returning a new `AsyncMock`.

But since `__aiter__()` is called without an `await`, then we get the
following exceptions/warnings:

* TypeError("'async for' requires an object with __aiter__ method, got
  coroutine")
* RuntimeWarning: coroutine 'AsyncMockMixin._execute_mock_call' was
  never awaited

To fix this, we just crate a proper fake async iterator we can return
to the async mock.

Signed-off-by: Leandro Lucarella <[email protected]>

Author: llucax

tests/test_client.py

@@ -36,6 +36,16 @@
 )
 
 
+class _FakeAsyncIterable:
+    def __aiter__(self) -> Any:
+        """Iterate over the fake async iterable."""
+        return self
+
+    async def __anext__(self) -> Any:
+        """Return the next item in the async iterable."""
+        raise StopAsyncIteration
+
+
 @dataclass
 class SetupParams:  # pylint: disable=too-many-instance-attributes
     """Parameters for the setup of the test suite."""
@@ -133,6 +143,10 @@ def set_up_order_detail_response(
 
 async def test_stream_gridpool_orders(set_up: SetupParams) -> None:
     """Test the method streaming gridpool orders."""
+    set_up.mock_stub.ReceiveGridpoolOrdersStream = AsyncMock(
+        return_value=_FakeAsyncIterable()
+    )
+
     set_up.client.gridpool_orders_stream(set_up.gridpool_id)
     await asyncio.sleep(0)
 
@@ -143,6 +157,10 @@ async def test_stream_gridpool_orders(set_up: SetupParams) -> None:
 
 async def test_stream_gridpool_orders_with_optional_inputs(set_up: SetupParams) -> None:
     """Test the method streaming gridpool orders with some fields to filter for."""
+    set_up.mock_stub.ReceiveGridpoolOrdersStream = AsyncMock(
+        return_value=_FakeAsyncIterable()
+    )
+
     # Fields to filter for
     order_states = [OrderState.ACTIVE]
 
@@ -162,6 +180,10 @@ async def test_stream_gridpool_trades(
     set_up: SetupParams,
 ) -> None:
     """Test the method streaming gridpool trades."""
+    set_up.mock_stub.ReceiveGridpoolTradesStream = AsyncMock(
+        return_value=_FakeAsyncIterable()
+    )
+
     set_up.client.gridpool_trades_stream(
         gridpool_id=set_up.gridpool_id, market_side=set_up.side
     )
@@ -177,6 +199,10 @@ async def test_receive_public_trades(
     set_up: SetupParams,
 ) -> None:
     """Test the method receiving public trades."""
+    set_up.mock_stub.ReceivePublicTradesStream = AsyncMock(
+        return_value=_FakeAsyncIterable()
+    )
+
     # Fields to filter for
     trade_states = [TradeState.ACTIVE]