Presubmit `showcase (3.13, showcase_w_rest_async, google)` fails at HEAD

[parthea]

Presubmit showcase (3.13, showcase_w_rest_async, google) fails at HEAD with the following failure:

........................................................................ [ 48%]
.....................................F.F................................ [ 97%]
....                                                                     [100%]
=================================== FAILURES ===================================
_________________ test_async_unary_stream_reader[rest_asyncio] _________________

async_echo = <google.showcase_v1beta1.services.echo.async_client.EchoAsyncClient object at 0x7fb1bc0fe9e0>

    @pytest.mark.asyncio
    async def test_async_unary_stream_reader(async_echo):
        content = "The hail in Wales falls mainly on the snails."
        stream = await async_echo.expand(
            {
                "content": content,
            },
            metadata=_METADATA,
        )
    
        # Note: gRPC exposes `read`, REST exposes `__anext__` to read
        # a chunk of response from the stream.
        response_attr = (
            "__anext__" if "rest" in str(async_echo.transport).lower() else "read"
        )
    
        # Consume the response and ensure it matches what we expect.
        for ground_truth in content.split(" "):
>           response = await getattr(stream, response_attr)()

tests/system/test_streams.py:133: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
.nox/showcase_w_rest_async-3-13/lib/python3.13/site-packages/google/api_core/rest_streaming_async.py:79: in __anext__
    raise e
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <google.api_core.rest_streaming_async.AsyncResponseIterator object at 0x7fb1bc1cdd10>

    async def __anext__(self):
        while not self._ready_objs:
            try:
>               chunk = await self._response_itr.__anext__()
E               StopAsyncIteration

.nox/showcase_w_rest_async-3-13/lib/python3.13/site-packages/google/api_core/rest_streaming_async.py:73: StopAsyncIteration

The change is related to google-auth 2.40.0 released yesterday.

The issue is that the response is read in the auth library via the new code await response.json() which was added, and as a result, when tests run there is no response left to read.

https://github.com/googleapis/google-auth-library-python/blob/0bebddda369b27b5ec4acec2073310b0b8a35461/google/auth/aio/_helpers.py#L39

There is a breaking change, since code works prior to 2.40.0

[parthea]

To reproduce this problem, make the following change and run nox -s showcase_w_rest_async-3.9

py3133partheniou@partheniou-vm-3:~/git/gapic-generator-python$ git diff
diff --git a/tests/system/test_streams.py b/tests/system/test_streams.py
index 38a2e477..6e589f20 100644
--- a/tests/system/test_streams.py
+++ b/tests/system/test_streams.py
@@ -21,6 +21,8 @@ from google import showcase
 
 _METADATA = (("showcase-trailer", "hello world"),)
 
+import os
+os.environ["GOOGLE_SDK_PYTHON_LOGGING_SCOPE"]="google"
 
 def test_unary_stream(echo):

[parthea]

Filed googleapis/google-auth-library-python#1754 to report this problem upstream