Background

test/asynchronous/test_async_network_layer.py has two tests that directly append to protocol._pending_messages (a private deque) to stage state before exercising buffer_updated and close:

• test_buffer_updated_completes_pending_future (line 105)
• test_close_with_exception_propagates_to_pending (line 115)

Problem

This is white-box coupling to an internal data structure. If _pending_messages is ever replaced with a different internal mechanism (e.g., a dict keyed by request ID), these tests break even though the observable behaviour of PyMongoProtocol is unchanged.

Fix

Replace the direct _pending_messages.append(future) setup with calls to protocol.read(), which enqueues the waiter through the public API and makes the tests resilient to internal refactors.

Discovery

Found during code review of PR #2774 (coverage increase for network_layer.py).